APPENDIX

The geography of the brain

It is useful, when studying the brain, to divide it into different regions. Some of them are delineated by grooves or clefts. Using this method, the cerebral cortex, which includes the entire surface of the cerebral hemispheres, can be divided into four large regions: frontal, parietal, occipital and temporal. The parietal and frontal cortices, for example, are separated by the central sulcus. Each of these large regions of the cortex takes part in multiple functions but, at the same time, has a certain degree of specialization. The frontal cortex functions as the brain’s ‘control tower’. Without it, for example, we would be unable to refrain from eating in a situation in which we know it is not good for us (although we are hungry). The frontal cortex regulates, inhibits and operates different cerebral processes, and makes plans. The occipital cortex manages visual perception. The parietal cortex integrates and coordinates sensorial information with actions. It accounts for our ability to catch a ball by guiding our movements using in-real-time information about its speed and its trajectory. And the temporal cortex encodes memories, and works as a bridge between vision, hearing and language.

These large regions are in turn divided according to anatomical criteria or functional roles. For example, the motor cortex is the area of the frontal cortex that manages the muscles, and the somatosensory cortex is the area in the parietal cortex that coordinates tactile perception.

In the fissure that separates the two hemispheres of the brain, we can identify subdivisions of the frontal cortex. For example, the ventromedial prefrontal cortex and the orbitofrontal cortex are involved in different aspects of decision-making such as encoding the value and the risk of different options. The cingulate cortex extends beneath the frontal and parietal cortices. The section closest to the forehead (anterior cingulate) plays a primordial role in the ability to monitor and control our actions. For instance, when you realize you have made a mistake just after making an action, it is because the anterior cingulate has signalled it. On the other hand, the posterior cingulate (the part closest to the nape) activates when your mind wanders or when you are daydreaming. Finally, in the centre of the brain is the thalamus, which turns off when you are asleep or under anaesthesia, and it turns on when you wake up.