Chapter 10. Neuroscience and Older Drivers

Maria T. Schultheis and Kevin J. Manning

Drexel University, Philadelphia, PA, USA

The number of older drivers on the road continues to increase, providing evidence that individuals are staying on the road later in life. The desire to remain an active driver is not surprising given the fact that in our current society the loss of the driving privilege can have significant negative ramifications. The inability to drive an automobile can affect an individual's everyday activities (e.g., getting to work, opportunity to engage in social activities, and access to medical appointments/needs) and overall sense of autonomy. Not surprisingly, as the number of older drivers increases, there are also growing concerns regarding the overall ability and safety of these individuals on the road. Research on older drivers can be roughly categorized into two primary areas: studies examining driving among the normal aging population and studies examining older drivers with medical conditions (e.g., dementia). The key distinction between the two is the differences in the neurological and/or neuropathological status of the study population. Although areas of concern in relation to driving have been acknowledged for both groups, some differences can be identified based on the level and type of neurological compromise. This chapter provides an introduction to this comprehensive literature and a brief overview of underlying neurological involvement and the resulting cognitive impairments. It also discusses the application of these impairments to driving ability in common medical populations of older adults (i.e., stroke and Alzheimer's disease).

1. Neuroscience and Older Drivers

Cognitive neuroscience of aging is a multifaceted discipline that encompasses clinical neuropsychology, cognitive neuroscience, and cognitive aging (Cabeza et al., 2005 and Grady, 2008). Advances in technology, such as structural and functional neuroimaging, have contributed a growing body of literature that has better defined the overall changes in the aging brain. Specifically, research has been extremely informative regarding the age-related differences (i.e., cross-sectional research) and age-related changes (i.e., longitudinal research) in brain structure and function.

1.1. The Effect of Aging on Neuroanatomy and Cognition

As individuals age, physiological changes to the brain occur. In general, brain volume is reduced through atrophy and subsequent enlargement of the cerebral ventricles, or ventriculomegaly (Raz, Gunning-Dixon, Head, Dupuis, & Acker, 1998). Specifically, cross-sectional studies of normative cohorts reveal that the majority of brain structures demonstrate reduced volume, including the cerebral gray (i.e., neurons) and white (i.e., axons) matter, as well as subcortical structures, such as the hippocampus and major elements of the basal ganglia (Raz & Rodrigue, 2006). The rate of ventricular expansion and shrinkage of the total brain parenchyma (atrophy) accelerates with age and appears to follow a linear course. The volume of the white matter, especially in the prefrontal regions (Raz et al., 2005), follows a nonlinear longitudinal course, with linear increase until young adulthood, plateau during middle age, and decline in later years.

This overall cerebral atrophy of gray and white matter is thought to explain much of the cognitive changes seen in all adults as they age. For example, it is hypothesized that atrophy of the brain's frontal lobes' gray matter and its surrounding white matter connections may be the underlying neuropathology of observed mild memory difficulties in aging. Behaviorally, this mild impairment may be most apparent on tasks demanding high levels of attention and executive functioning. An overall “slowing” of behavior is a universal description associated with aging (Salthouse, 1996), which has been related to white matter changes (Gunning-Dixon & Raz, 2000) in the brains of healthy adults.

In particular, among normal aging adults, atrophy of the frontal lobes has been a robust and consistent finding (Haug and Eggers, 1991 and Raz et al., 1998). Researchers have suggested that this change in frontal lobe physiology may lead to subtle changes in inhibitory control, leading to observed declines in performance on tests of executive function (i.e., problem solving and decision making). In addition to general “executive functioning decline,” working memory, another important cognitive construct associated with the frontal lobes, has also been shown to decline among normal aging adults. Of note, working memory serves as an important link to slowed processing speed (Gunning-Dixon & Raz, 2000).

From a broader and simpler perspective, cognitive functions can be conceptualized and categorized into two general aspects: (1) crystallized intelligence, which includes overlearned, familiar skills accumulated through education and practice, and (2) fluid intelligence, which includes nonverbal reasoning, motor tasks, and problem-solving abilities that evolve and change as a result of physiologic maturation. It has been theorized that crystallized abilities, such as knowledge of general facts and vocabulary, sharply increase during the early years of formal education and then stabilize or gradually improve throughout adulthood. By contrast, fluid abilities are theorized to improve throughout childhood and then gradually decline in adult years, with more rapid deterioration in old age due to neuronal loss, changes in physiologic brain function, and increased rates of disease and injury. Research employing both cross-sectional and longitudinal designs has supported the relative stability of verbal abilities with advancing age (i.e., crystallized) and the decline in tasks requiring perceptual speed, selective attention, and complex problem solving (i.e., fluid) (Tucker-Drobb & Salthouse, 2008).

1.2. Age-Related Changes in Cognition Relevant to Driving

A clinical priority of research on driving with older adults is the identification of deficits associated with specific diagnosis (e.g., Alzheimer's disease). However, it can be argued that diagnosis alone does not render an individual unfit to drive. Certainly, the driving of individuals with a neurodegenerative illness should be monitored because their cognitive abilities will change and/or decline to the level that may prohibit driving. However, as evidenced by studies examining healthy older adults, cognitive abilities necessary for safe driving can be disrupted in older adults without dementia as well.

In an analysis of moderately cognitively impaired adults with an average age of 76 years (Average Mini-Mental State Exam=25; range, 14–30), performance on a test of clock drawing highly correlated with total number of driving errors using a driving simulator (r=0.68) (Freund, Gravenstein, Ferris, Burke, & Shaheen, 2005). The authors hypothesized that this may be “because executive functioning is a critical component of safe driving, in the presence of executive dysfunction, the automatized and procedural skills learned over decades of daily living do not protect the older driver from errors” (p. 243). Hypothetically, subtle executive changes in a more cognitively intact group may show a stronger relationship with cognitively demanding driving tasks.

Other authors have reported data suggesting a relationship between executive functioning and driving. Whelihan, DiCarlo, and Paul (2005), using a mixed sample of older adults with questionable dementia and brain injury, found that out of a comprehensive neuropsychological battery, only performance on a maze navigation test, time to complete Trail Making Test Part B, and the Useful Field of View (a measure of visual attention) correlated with driving ability as measured by a road test. Together, these three measures explained 46% of the variance in a total composite of the road test (Whelihan et al., 2005). Ott et al. (2003) found maze performance to be predictive of driving ability; this was the sole measure from a comprehensive battery of tests to be associated with caregiver ratings of driving performance in individuals with Alzheimer's disease (AD). Finally, Daigneault, Joly, and Frigon (2002) found that older adults with a history of accidents were more impaired on four measures of executive functioning: Trail Making Test, Wisconsin Card Sorting, Stroop Color Word, and Tower of London.

Taken together, these findings suggest that normally occurring changes in cognitive status may be relevant to driving performance. In particular, cognitive functions often grouped as “executive functions” consistently appear to be important; these include cognitive domains such as information process speed, working memory, decision making, and visual problem solving. Although medically diagnosed older adults may demonstrate more significantly impaired levels of these domains, the fact remains that driving capacity appears to be affected when changes in these domains occur.

The increasing amount of evidence supporting the relationship between aging and cognitive deterioration has led to policy discussions about mandatory aged-based and disorder-based assessments. To further explore reception for this, Adler and Rottunda (2010) investigated the attitudes, beliefs, and preferences of older adults, law enforcement officers, and licensing authorities toward re-examination of driving skills for people with AD and Parkinson's disease (PD) and at varying ages. The results indicated strongest support across all groups for retesting for those with AD but only moderate endorsement of re-testing for those with PD. Moderate support was also given for re-testing of 90-year-old drivers, and the least support was given for reassessment of 70-year-old drivers (Adler & Rottunda, 2010).

1.3. What are the Characteristics of Older Drivers?

In the literature, driving performances have been defined using a variety of measures, including traffic crashes and the behind-the-wheel (BTW) exam. Population-based studies of driving in older adults have typically used number of traffic crashes as the outcome variable representing driving performance (Langford, 2008). McGwin and Brown (1999) compared the characteristics of crashes among young, middle-aged, and drivers older than age 55 years from all of the police-reported traffic crashes in the state of Alabama during 1996. Compared to young and middle-aged drivers, older drivers were more likely to be involved in crashes at intersections, fail to yield the right of way, and fail to heed stop signs or signals. Crashes occurring while turning and changing lanes were also more common among older drivers. By contrast, older drivers were less likely to have crashes during adverse weather and while traveling at high speeds. Other studies have reported similar crash characteristics among older adults (Cooper, 1990, Hakamies-Blomqvist, 1993 and Ryan et al., 1998).

A plethora of research demonstrates the significant association between crash risk in older adults and cognitive test performance on tests of attention, memory, executive functioning, and processing speed (Ball et al., 1993, Lafont et al., 2008, Staplin et al., 2003 and Stutts et al., 1998). Despite statistical significance, the clinical significance of the association between cognitive test performance and crash risk is poor. For example, Carr, Duchek, and Morris (2000) compared 63 healthy older adults and 58 individuals with clinically diagnosed AD and found no group difference in the number of accidents 5 years prior to the onset of the study. In other words, despite impairment in various domains of functional capacity severe enough to warrant a diagnosis of AD, adults with the disease would show no differences in functional capacity if functional capacity were measured using only driving accidents. The point is that although the statistical association between cognitive test performance and crash risk may be beyond a chance possibility, it provides little clinical value in determining individuals who should limit or relinquish their driving privileges (Bedard, Weaver, Darzins, & Porter, 2008). This is likely due to the rarity of accidents and the fact that they represent a heterogeneous collection of incidents occurring in a multitude of circumstances (McGwin & Brown, 1999). More sensitive measures of driving capacity are needed to distinguish older adults with obvious gross functional and cognitive impairment from healthy controls.

Currently, the clinical “gold standard” of driving ability is the BTW driving evaluation. The BTW consists of route following, or the examiner directing the examinee where to drive next, and is similar to the “road test” that most individuals undergo to receive their driver's license. However, when considering its utility as an outcome measure, similar to “number of traffic crashes,” the BTW lacks sensitivity to detect subtle changes in driving performance. Kay, Bundy, Clemson, and Jolly (2008) made this point in their investigation of the psychometric properties of a standardized BTW with 100 cognitively intact older drivers aged 60–86 years. Although the authors found total driving errors and overall ratings of performance (i.e., pass/fail) to be valid and reliable indicators of driving safety, these scoring systems were not sensitive enough to determine different levels of driving ability or even discriminate “safe” versus “unsafe” drivers (Kay et al., 2008). Similar findings have been found for older adults with dementia. Ott et al. (2008) conducted a longitudinal study of drivers with AD spanning 3 years using the BTW. Greater severity of dementia, increased age, and lower education were associated with higher rates of BTW failure at follow-up. However, only 22% of individuals with mild AD failed the BTW at follow-up. The failure rate was even less in the group of individuals considered to have questionable dementia or mild cognitive impairment.

On a practical level, in an attempt to harness this research information for clinical applications, the American Medical Association (2010) compiled physician guidelines for the assessment and counseling of older drivers. These guidelines include recommendations for specific tests for the Assessment of Driving-Related Skills (ADReS), including visual measures (i.e., visual acuity and visual fields) and basic cognition (Trail Making A and B Test and Clock Drawing Test).

2. Medical Issues and Older Drivers

2.1. Driving and the Dementias

Without doubt, the dementing conditions are among the most problematic faced by aging drivers. In addition to affecting cognitive and visuomotor abilities that can impact everyday activities such as driving, the dementing illnesses can also deprive individuals of the judgment and insight needed to accurately assess their own declining abilities and increase risk due to these deficits. At the same time, many dementing conditions are progressive and tend to be insidious, making detection more difficult for patients, families, and health care professionals.

Alzheimer's disease is the most common cause of dementia and the sixth leading cause of death. Women are more likely than men to have AD, and it has been estimated to affect 14% of all people aged 71 years or older. AD is a steadily progressive disorder that is characterized by a variety of cognitive function abnormalities. By definition, diagnosis of dementia requires the objective measurement of impairments in memory and one other cognitive domain that is resulting in a negative impact on occupational or social functioning (American Psychiatric Association, 2000). One of the common activities of daily functioning that is included is driving an automobile.

Competence in driving a motor vehicle has implications both for the safety of the individual affected by dementia and for other road users. Therefore, it is not uncommon for health care providers to have to determine whether individuals with dementia are able to continue to drive and/or when they should stop driving. Retrospective surveys concerning driving and dementia suggest that many patients diagnosed with dementia do continue to drive and may be reluctant to give up driving (Friedland et al., 1988 and Gilley et al., 1991). In 2000, Dubinsky, Stein, and Lyons reported an eightfold increase in the crash rate for a group with AD, implying a greater risk of crashes for drivers with AD compared to other drivers. It is also noteworthy that two early retrospective studies found that only 50% of drivers with AD had ceased driving within a 3-year period of the onset of dementia (Drachman and Swearer, 1993 and Friedland et al., 1988), after which time crash risk increases substantially. Tuokko, Tallman, Beattie, Cooper, and Weir (1995) examined driving records (insurance claims) of 165 drivers with dementia and found that they had an approximately 2.5 times higher crash rate than that of the matched control sample. In contrast, in a study using state records, road crash and violation rates among AD patients did not differ significantly from those of matched controls (Trobe, Waller, Cook-Flannagan, Teshima, & Bieliauskas, 1996). However, this study did not control for mileage driven, and reduced driving exposure of AD patients may be the reason why their crash rate was equal to that of control subjects. Carr and colleagues (2000) reported that a sample of 63 drivers with very mild or mild Clinical Dementia Rating (Hughes, Berg, Danziger, Coben, & Martin, 1982) showed no difference in state recorded crash rate for the previous 5-year period compared to nondemented, older control drivers, even after adjusting for exposure. Carr et al. noted that the drivers with dementia in their study may have been only mildly impaired in their driving skills, with little, if any, impairment in driving skills evident in the preceding 5-year period.

It has been recommended that limitation of driving privileges should be based on demonstration of impaired driving competence rather than on a clinical diagnosis such as AD. As early as 1988, Drachman and colleagues argued that individuals with an AD diagnosis should not be excluded from driving based on the possibility of minimal functional decline in early AD. They also suggested that the likelihood of the loss of driving privileges may result in many people with mild or potentially treatable cognitive impairments refraining from seeking medical advice about continuing to drive. O'Neill et al. (1992) based their argument on findings of studies that demonstrated that a substantial percentage of patients with AD at the time of driving assessment had suffered no deterioration in driving skills, thus supporting the view that a diagnosis of AD alone is not sufficient to preclude driving. Indeed, researchers continue to attempt to define the rate of AD progression and nature of disease manifestation, particularly in the earlier stages; therefore, using a diagnosis of AD as a basis for a decision regarding driving is not recommended.

In 2000, the American Academy of Neurology published a practice parameter regarding AD and driving (Dubinsky et al., 2000). Two recommendations were made. First, drivers with AD who have a Clinical Dementia Rating (CDR) of 1.0 or greater should not drive because of driving performance errors and a substantially increased accident rate. Second, drivers with possible AD with a severity of CDR of 0.5 should be considered for referral for driving performance evaluation. Furthermore, because of the high likelihood of disease progression, it was recommended that dementia severity and appropriateness of continued driving be reassessed every 6 months. This follow-up recommendation was evaluated in a prospective longitudinal study of 58 healthy controls, 21 individuals with very mild AD, and 29 individuals with mild AD. In this study, participants underwent a standardized on-road test approximately every 6 months for a 3-year period. Analysis of the survival curves generated for each group supported the recommendation to conduct driver evaluations every 6 months for people with very mild and mild dementia of the Alzheimer's type (Duchek et al., 2003). Although helpful, there remains limited follow-up to the application of these initial guidelines, and additional longitudinal studies are needed to better describe the progression of AD and its subsequent effect on driving ability.

A 2010 update of these practice parameters attempted to provide more specific guidelines for clinicians (Iverson et al., 2010). The authors recommended that for individuals with dementia, (1) consideration of the CDR scale, (2) a caregiver's rating of a patient's driving ability as marginal or unsafe, (3) a history of crashes or traffic citations, (4) reduced driving mileage or self-reported situational avoidance, (5) Mini-Mental State Examination scores of 24 or less, and (6) aggressive or impulsive personality characteristics are useful for identifying patients at increased risk for unsafe driving. Although informative, the study excluded much of the work with neuropsychological testing and subsequently did not support or refute the contributions of cognitive testing—an important limitation that minimizes the relevance of cognitive status in this population.

Although these studies serve to provide clinicians with some guidelines, potential difficulties with implementation of these parameters have been noted. For example, the AD patient or his or her family may not accept the physician's recommendation for discontinuation of driving. Thus, although physicians have a significant responsibility to determine “medical” competence to drive, in practice such a clinical decision is difficult because of lack of standards and effective guidelines.

2.2. Other Dementias

Other less frequently occurring dementias include illnesses such as PD and Huntington's disease (HD). Much less is known about the relationship between these disorders and driving capacity. However, given some commonality (particularly in the cognitive domains), the use of similar strategies for evaluating driving that are employed for AD have been recommended.

2.2.1. Parkinson's Disease

This common disease, known since ancient times, was first clinically described by James Parkinson in 1817. The disease generally begins at 40–70 years of age, with the peak age of onset in the sixth decade. It is infrequent before 30 years of age, and most series contain a somewhat larger proportion of men. The core syndrome is one of expressionless face, poverty and slowness of voluntary movement, “resting” tremor, stooped posture, axial instability, rigidity, and festinating gait. Although most are familiar with the motor effects of the disease, cognitive decline may also be seen. Patients therefore not only experience a progressive loss of motor control but also eventually are at risk for cognitive and emotional deterioration. Cognitive symptoms include slowed information processing, executive dysfunction, memory loss, and associated personality changes (Aarsland et al., 2009 and Rodriguez-Oroz et al., 2009).

Work by Uc and colleagues has provided a greater understanding of the driving ability of individuals with PD (Rizzo, Uc, Dawson, Anderson, & Rodnitzky, 2010). In 2009, Uc and colleagues compared the performance of licensed drivers with PD with that of an age-matched control group. They found that overall, drivers with PD had poorer road safety compared to controls, but there was considerable variability among the drivers with PD, and some performed normally. Familiarity with the driving environment was a mitigating factor against unsafe driving in PD. Impairments in visual perception and cognition (attention, visuospatial, and visual memory) were associated with road safety errors in drivers with PD (Uc, Rizzo, Johnson, et al., 2009).

Another study examining driving ability found that drivers with PD made more safety errors than did neurologically normal drivers during a route-following task. The authors concluded that the PD group driver safety was degraded due to an increase in the cognitive load in patients with limited reserves. Driving errors and lower driver safety were also associated more with impairments in cognitive and visual function than with the motor severity of the disease in drivers with PD (Uc et al., 2006). This group of researchers also employed the use of driving simulation to better delineate the driving errors seen in PD. Using this methodology, they concluded that under low-contrast visibility conditions, drivers with PD had poorer vehicle control and were at higher risk for crashes (Uc, Rizzo, Anderson, et al., 2009), and that the quantitative effect of an auditory–verbal distracter task on driving performance was not significantly different between PD and control groups. However, a significantly larger subset of drivers with PD had worsening of their driving safety errors during distraction (Uc et al., 2006). Across the various studies, cognitive predictors of driving performance included visual processing speed and attention, motion perception, contrast sensitivity, visuospatial construction, motor speed, and Activities of Daily Living score.

2.2.2. Huntington's Disease

This disease, distinguished by the triad of dominant inheritance, choreoathetosis, and dementia, derives its eponym from George Huntington (1872). Although relatively rare, in university hospital centers this is one of the most frequently observed types of hereditary nervous system disease. The usual age of onset is in the fourth and fifth decades, but 3–5% of cases begin before the 15th year and some even in childhood. In 28% of cases, symptoms become apparent after 50 years. The progression of the disease is slower in older patients. Once begun, the disease progresses relentlessly.

The personality and psychiatric changes associated with HD assume several subtle forms long before the deterioration of cognitive functions becomes evident. In approximately half of the cases, alterations of character are the first symptoms. Patients begin to find fault with everything; they may be suspicious, irritable, impulsive, eccentric, untidy, or excessively religious; or they may exhibit a false sense of superiority. Poor self-control may be reflected in outbursts of temper, fits of despondency, alcoholism, or sexual promiscuity. Disturbances of mood, particularly depression, are common and may constitute the most prominent symptoms early in the disease.

Eventually, other cognitive functions deteriorate, and the patient becomes less communicative and more socially withdrawn. Diminished work performance, inability to manage household responsibilities, disturbances of sleep, difficulty in maintaining attention, impaired concentration, deficits in learning new material, and mental rigidity become apparent, along with loss of fine manual skills. Because memory performance benefits from cues to help with retrieval of information, HD has been characterized as a “subcortical dementia.” Increased deterioration of motor functions and chorea (a relatively ceaseless occurrence of a wide variety of rapid, highly complex, jerky movements that appear to be coordinated but are in fact involuntary) usually follow.

To date, only one study has empirically assessed the influence of the neurological and cognitive impairments of HD on automobile driving (Rebok, Bylsma, Keyl, Brandt, & Folstein, 1995). These authors found that HD patients performed significantly worse than control subjects on driving-simulator tasks and were more likely to have been involved in a collision in the preceding 2 years (58% of HD patients vs. 11% of control subjects). Patients with collisions were less functionally impaired but had slower simple reaction time scores than did those without collisions. Although additional research is needed, to date there is a presumption that such patients will eventually cease driving as this terminal disease progresses.

It is remarkable that other systematic studies examining driving performance in this population are lacking, despite the fact that this is a progressive disease with known cognitive impairments. In particular, difficulties with divided attention, executive functioning, and awareness have all been identified as potential cognitive contributors to driving difficulties in this population. As is the case with other dementias, there is no uniform national law about driving with HD, but several support organizations directly address the topic of driving and offer recommendations for modifying driving behaviors (http://hopes.stanford.edu/n3547/managing-hd/lifestyle-and-hd/driving-and-huntingtons-disease).

2.3. Cerebral Vascular Accidents or Stroke

Cerebral vascular accidents or strokes are the third leading cause of death in the United States. By definition, a stroke occurs as a result of blockage or hemorrhage of a blood vessel leading to the brain. The resulting lack of oxygen supply to the brain results in damage that can manifest in a variety of physical, cognitive, and behavioral deficits for the individual. Common difficulties can include hemiparegia or paralysis of upper and lower extremities, speech difficulties, visual perception and visual spatial difficulties, and changes in cognition (e.g., memory and attention). Not surprisingly, these deficits can have a significant impact on an individual's activities of daily living and overall quality of life.

Given the high value placed on individual transportation in the United States, it is not surprising that many individuals seek to return to driving after experiencing a stroke. In fact, it is estimated that approximately 30–50% of stroke survivors return to driving (Fisk et al., 2002, Fisk et al., 1997 and Heikkila et al., 1999). However, it has also been reported that many stroke survivors do not go through any formal evaluation of their driving ability or receive advice before returning to the road. Therefore, the challenge remains in determining how the various sensorimotor and cognitive impairments resulting from stroke may or may not impact the individual's performance on the road. To date, although no single measurement can be used to definitively calculate an individual's driving capacity, much has been learned about driving after stroke.

It is well documented that stroke can result from different etiologies and can present in significantly varying degrees of severity. As a result, stroke is a major cause of disability, affecting approximately 500,000 individuals annually. Although the highest incidence is reported in older adults, work has identified an increasing number of younger adults who suffer from strokes (Bjorkdahl & Sunnerhagen, 2007). Given this fact, it is not surprising that stroke survivors (both young and older) find that driving cessation interferes with activities related to independent living (e.g., working) and consider the resumption of driving after stroke an important step in their recovery. Long-standing evidence supporting this finding first came from studies that demonstrated that stroke survivors who did not resume driving participated in fewer social activities and were more likely to be depressed (Legh-Smith, Wade, & Hewer, 1986). In addition, one study that focused on driving resumption after mild stroke found that 50% of individuals returned to driving within the first month after experiencing a stroke (Lee, Tracy, Bohannon, & Ahlquist, 2003), further underscoring the need for early assessment. Indeed, accuracy in measuring driving safety after stroke is crucial for ensuring that individuals who are safe drivers are not prevented from maintaining their independent mode of transportation and for preventing individuals who are unsafe drivers from posing a danger to themselves and others.

Several studies have documented that of individuals who drove before their stroke, approximately 30–59% return to driving after their stroke (Fisk et al., 1997 and Heikkila et al., 1999). Of those individuals returning to driving, almost one-third report high driving exposure, driving 6 or 7 days per week and/or 100–200 miles per week (Fisk et al., 1997). However, other findings indicate that stroke survivors drive less compared to a nonstroke cohort (Fisk et al., 2002). Specifically, although no differences in days per week of driving were seen, nonstroke drivers drove to more places, took more trips, and drove more miles (Fisk et al., 2002). Drivers who returned to driving also acknowledged difficulties in varying driving situations, such as making left turns, driving on the interstate, and driving in heavy traffic. Despite this, the stroke drivers did not differ from the nonstroke drivers in occurrences of self-reported crashes or citations (Fisk et al., 2002). Overall, stroke drivers appear to be self-regulating their driving behaviors and exposure.

2.3.1. Right Versus Left

One of the most common areas of stroke research is evaluating differences in impairment resulting from strokes in the two hemispheres. Several studies have examined the lesion location and the extent of brain damage incurred to better determine the impact of the resulting impairments on driving performance. Cortical damage in the area of the temporoparietal lobe of the right hemisphere often results in impairments in spatial and perceptual abilities and also attentional and visual skills deficits such as visual neglect. Physically, a right-hemisphere stroke can often lead to paralysis of the left side of the body, known as left hemiplegia. In contrast, cortical damage to the left hemisphere often results in language and speech difficulties and paralysis of the right side of the body, known as right hemiplegia. More global cognitive deficits, such as changes in memory and attention, cannot be exclusively associated with one or the other hemisphere. In relation to driving difficulties, several studies have indicated poorer performance in individuals who have sustained a right-hemisphere stroke (Fisk et al., 2002, Korner-Bitensky et al., 2000 and Quigley and DeLisa, 1983). These researchers have noted the impact of visual spatial and perceptual deficits on driving capacity.

Although physical impairments can lead to problems with motor reaction time, which can be crucial in driving (e.g., braking) and safe maneuvering (e.g., steering), in many cases, adaptive driving equipment can be used to minimize the impact of physical limitations. For example, an adaptive spinner knob can be attached to the steering wheel to allow controlled steering with the use of only one hand, or a left-foot gas or pedal may be used if the individual is unable to use his or her right foot to push the accelerator or brake. In fact, Smith-Arena, Edelstein, and Rabadi (2006) found that individuals in an acute rehabilitation setting with higher Motricity Index scores and intact visual fields were more likely to pass an in-clinic driver evaluation. The researchers concluded that physicians could safely identify post-stroke patients most appropriate for driver evaluation when mild physical impairments, normal visual fields, and mild cognitive impairments were present. In summary, although physical challenges resulting from stroke can impact driving performance, cognitive and visual impairments pose a greater challenge for returning to driving.

2.3.2. Cognition and Perception

Stroke can produce a variety of cognitive difficulties that can affect an individual's ability to return to driving, including slowed information processing speed, visuospatial and perceptual deficits, visual inattention, decreased ability to concentrate, and reasoning difficulties. As a result, cognition and driving after stroke has been extensively studied, with the main goals being to better define this relationship and to identify potential cognitive predictors of driving performance. To date, research has not defined a specific cognitive impairment pattern that is predictive of driving performance, but the results of these studies have identified specific cognitive domains relevant to driving, and some new computerized and noncomputerized driving assessment tasks designed to assess the cognitive domains of driving after stroke have been generated.

One of the most common problems associated with stroke and a cognitive domain identified early on as relevant to driving concerns perceptual abilities (Quigley and DeLisa, 1983 and Sivak et al., 1981). Early studies examining perceptual/cognitive abilities among right- and left-hemisphere stroke survivors indicated that individuals with right-hemisphere strokes demonstrated the most severe perceptual difficulties. Of those who returned to driving, when self-reported traffic difficulties (e.g., accident involvement) were examined 1 year later, the predictive validity of the perceptual assessment procedure held true for approximately 80% of the sample (Simms, 1985).

Another study used a factor analysis approach to better define the perceptual/cognitive constructs of driving performance by conducting a comprehensive neuropsychological battery on 72 consecutively referred patients who had suffered a stroke (Sundet, Goffeng, & Hofft, 1995). The test battery was factor analyzed into four valid principal components: visual perception, spatial attention, visuospatial processing, and language/praxis. The researchers reported greater visual neglect in right-hemisphere strokes compared to left-hemispheres strokes, but they did not find overall group differences in the number of patients denied driving after a stroke. They concluded that in addition to hemianopia, measures of neglect, speed of mental processing, and emotional disturbances such as denial of illness were the most potent subject characteristics in assessing patients for return to driving (Sundet et al., 1995).

Mazer, Korner-Bitensky, and Sofer (1998) examined the use of perceptual tests to predict driving performance in individuals with stroke. Driving performance was quantified as pass or fail outcome of an on-road driving evaluation that was conducted by an occupational therapist and was based on observed driving behaviors. Their results indicated that a test of visual perception skills (Motor Free Visual Perception Test (MVPT)) was the most predictive of on-road performance (positive predictive value=86.1%; negative predictive value=58.3%), and that the combination of the MVPT and a measure of task switching (Trail Making Test Part B) represented the most predictive and parsimonious model for predicting on-road performance.

Other researchers have reported that a neuropsychological assessment including tests measuring dynamic cognitive processing and complex speed can be useful in assessing driving skills after stroke. For example, Lundqvist, Gerdle, and Ronnberg (2000) reported that complex reaction time the Stroop Color and Word Test, the Listening Span task, and a computerized administration of the K-test were most associated with driving skills, as defined by both on-road and simulated driving performance. Similarly, other researchers have found that although the MVPT is believed to be a strong predictor of on-road evaluation failure, its predictive validity is not sufficiently high to warrant its use as the sole screening tool in identifying those who are unfit to undergo an on-road evaluation (Korner-Bitensky et al., 2000).

As the challenge of determining driving capacity following a stroke has been acknowledged, it is not uncommon for many settings to rely on a team of clinicians who evaluate varying aspects of an individual's ability (e.g., medical and cognitive). One retrospective study, which attempted to better define the contributing factors to a team's decision on driving ability, examined 104 individuals who had suffered a first stroke (Akinwuntan et al., 2002). The researchers administered both a comprehensive predriving assessment and an on-road test. The predriving assessment included specific measures of vision (monocular vision, binocular vision, stereoscopy, and kinetic vision) and a neuropsychological assessment consisting of eight different tests: the Rey Complex Figure Test, UFOV, divide attention, flexibility, visual scanning, incompatibility, visual field, and neglect (Akinwuntan et al., 2002). Using logistic regression, the researchers found that a model including the side of lesion, kinetic vision, visual scanning, and a road test was the predictor of the team decision; within this model, the road test was the most important determinant. A combination of visual acuity and the Rey Figure test was the best subset for predicting on-road test performance (Akinwuntan et al., 2002). In follow-up prospective studies, these researchers found that a combination of visual neglect, Rey Figure, and on-road test was the best predictor of fitness to drive (as defined by clinicians' ratings) (Akinwuntan et al., 2006). The accuracy of this short battery was confirmed in another study demonstrating an 86% predictive value of these three tests, which are both sensitive (77%) and specific (92%) in their prediction (Akinwuntan et al., 2007). Taken together, these studies clearly indicate that the determination of driving after stroke cannot be limited to a single cognitive domain.

2.3.3. Aging and Stroke

In addition to coping with residual deficits of a stroke, many older adults must cope with ongoing cognitive and physical changes that are commonly seen in aging adults, such as decreased physical mobility, changes in vision, and changes in cognition (e.g., memory problems). Older individuals are also at risk for other neurological involvement; they may be at risk for additional strokes, other cardiovascular disorders, and/or injuries.

3. Other Considerations for Older Drivers

3.1. Medication

A peripheral challenge in considering the driving ability of older adults is the issue of polypharmacy or the use of multiple types of medications. Not surprisingly, as individuals age, there are higher risks for multiple types of medical issues, including systemic (e.g., diabetes), focal (e.g., cardiac and stroke), or emotional (e.g., depression). Treatment of these often coexisting diagnoses often results in the individual taking multiple medications. Subsequently, the older adult is at risk for taking concomitant medications, which can lead to serious drug interactions.

3.1.1. Emotional Impairment and Self-Awareness

Individuals who are unable to drive may suffer increased isolation, which may contribute to depression (Martolli et al., 2000). In addition to the physical limitations that can affect one's life after stroke, one's professional and personal lives are also tested and stressed. Many people who have suffered from stroke are unable to return to work in the same capacity as that prior to their disability. The disability not only affects the inflicted person but also the person's close inner circle. For example, there is more dependence on spouses/family members/close friends for basic everyday activities, such as eating, personal hygiene, and dressing.

It is also well-known that stroke patients may have problems recognizing their own cognitive or psychomotor disorders, and they may have serious impairment of functions that are crucial for safe driving. Particularly, damage to the nondominant hemisphere often causes anosognogia and neglect syndrome and, hence, lowered awareness. Heikkila et al. (1999) found that both patients and their spouses demonstrated a clear tendency to overestimate driving ability compared to the estimates of the neurologist and psychologist.

3.1.2. Education (for the Patient and for the Clinician)

As reported in even the earliest study by Quigley and DeLisa (1983), part of the rehabilitation team's efforts is directed toward providing the candidate with information about the policies and restrictions of the department of motor vehicles. However, Kelly, Warke, and Steele (1999), who investigated the awareness of patients and doctors of medical restrictions to driving, found that educating the client may be difficult. In addition to patients having difficulty knowing if they should drive based on their medical condition, Kelly et al. found that doctors had very poor knowledge of the current licensing policy and action to be taken if a patient was not eligible to drive. Medical staff does not seem to be able to provide this guidance. To increase doctors' awareness of medical restrictions to driving, greater emphasis must be placed on this aspect of patient care during both undergraduate and postgraduate training (Kelly et al., 1999).

With the growing need to improve older adult driving safety, different training strategies are beginning to emerge that focus on changing driving behaviors and knowledge. In 2007, Tuokko, McGee, Gabriel, and Rhodes examined the perceptions of risk, beliefs and attitudes, and openness to change of 86 older participants who voluntarily attended a driver education program. The authors reported that most people attending these sessions were not necessarily concerned about their own driving, safety, or abilities but were interested in maintaining mobility. They were conservative and reasonably consistent in their attitudes toward traffic regulations and safe driving practices. Some gender differences emerged, with more men than women being resistant to changing their driving habits and reporting that they drive after consuming alcohol, and more women than men identifying a role for their families in decision making regarding driving cessation. This suggests that educational material may need to be targeted differently for men and women and that psychosocial factors related to driving, such as driver perception, beliefs, and openness to change, will be useful for maximizing the fit between education program content and outcomes (Tuokko et al., 2007).

4. Conclusion

This chapter provided an introduction to the current literature on older drivers with and without neurological compromise. A main focus was providing information relevant to common clinical diagnoses in older drivers (e.g., dementia and stroke). Although much has been accomplished in this area, much work is needed. In particular, as new technologies (e.g., functional neuroimaging) provide greater insight into the neuroanatomy of aging and neurological compromises, we will be better able to understand the relationship between behavior and brain changes in older drivers. Given the growing number of older adults (and the anticipated continued growth), the need to increase our knowledge is clear.

The ability to drive is often synonymous with autonomy, and older drivers in our fast-paced society will likely continue to have a high reliance on automobiles in order to maintain their independence in their communities. The challenge posed to clinicians and driving experts is the ability to balance between an individual's autonomy and safety (both for the individual and for others). Given the known consequences of neurological compromise, the challenge that remains before us is to identify and refine the best methods to accurately make driving recommendations. In doing so, we can keep our roads and older drivers safe.

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