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The frontal cortex and social interaction
The frontal cortex seems to play an important role in the interpretation of visual information, such as that conveyed by faces. It has been known for many years that damage to the frontal lobes leads to a disruption of emotional and social behaviour. A particularly wellknown example is the case of Phineas P. Gage. Phineas was a 25-year old construction foreman for the Rutland and Burlington Railroad Company in New England. In 1843, in order to lay new railway tracks across Vermont, the railroad company carried out controlled blasting to level the uneven ground. Phineas was in charge of this blasting. His job was to drill holes in the rock, partially fill them with explosive powder, cover the powder with sand, and then tamp it down with an iron rod before laying a fuse. On the 13th of September, Phineas made a mistake. In a moment of abstraction, he began tamping directly over the explosive powder, before his assistant had covered it with sand. The resultant explosion threw the finepointed, 3 cm thick, 109 cm long tamping rod up into the air like a javelin and it landed several yards away. Unfortunately, Phineas had been bending over the tamping rod and during its trajectory it passed through his face, skull and brain. Although he was initially stunned, he rapidly regained consciousness and was able to talk, and even walk away from the site of his injury, if a little unsteadily. However, subsequently he was a changed man. Prior to his injury he had been an intelligent, responsible, socially welladapted individual. Subsequent to his injury, although his intelligence and other faculties were unimpaired, he became unreliable and offensive, with no respect for social conventions. He lost his job and led a wandering, transient existence until his death 12 years later. No autopsy was performed, but his skull (and the fateful tamping rod) were recovered for science, and have been on display at the Warren Anatomical Medical Museum at Harvard University (Figure 9.6).
A team led by Damasio has tried to calculate the brain areas damaged in the accident, based on the skull and the contemporary account of the attending physician, Dr John Harlow (Damasio et al., 1994). They conclude that damage was limited to the ventromedial region of both frontal lobes (an area called the orbitofrontal cortex or OFC), while the dorsolateral region was spared (Figure 9.5). This pattern of damage has been found in modern patients who have an inability to make rational decisions in personal and social matters, and are impaired in processing emotion. This effect is particularly marked in people who have suffered damage to this region early in life. In addition to the impairments in social interaction shown by patients who suffered OFC damage as adults, the behaviour of earlyonset patients includes stealing and violent assaults (Anderson et al., 1999). In many ways the early-onset patients resemble psychopathic
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Figure 9:6: View of the proposed position of the tamping rod in the skull and brain of Phineas Gage (redrawn from Damasio et al., 1994).
individuals, who are characterised by high levels of aggression and antisocial behaviour performed without guilt or empathy for their victims (Dolan, 1999). Damasio has suggested that emotion, and its underlying neural substrate participate in decision making within the social domain, and that an important site for this process is the OFC. This region has reciprocal connections to subcortical structures, such as the amygdala and hypothalamus, which control basic biological regulation, the processing of information on emotion and social cognition. As the case of the early-onset OFC patients demonstrates, early damage to the OFC disrupts this integration and thus the acquisition of the specific forms of knowledge necessary for regulating inter-personal and social behaviour.
Faces as a social semaphore
The primate face has undergone a remarkable transformation. Its neural innervation, musculature and flexibility have increased extensively, from the almost rigid mask of some New World monkeys to the flexible, highly mobile face of the great apes, which reaches its height of sophistication and elaboration in humans. What is the point of it all? It is not simply for identification purposes: a pattern of facial features unique to an individual need not be mobile to signal his or her identity. It seems that, as primates have developed more complex social groups, the primate face has developed into a kind of semaphore system, capable of signaling a wide range of complex social information. The recognition and interpretation of these social
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cues are extremely important for the smooth functioning of a social group and for an individual’s place within the hierarchy of this group. The increasing complexity of facial musculature and innervation seems to have been paralleled by an increasing sophistication of the neural representation of facially signaled information. However, there is strong evidence for a dissociation between recognition of facially conveyed information, such as identity and emotion, and the interpretation of this information. In both humans and monkeys, the recognition component seems to occur in the temporal visual cortex, whereas interpretation seems to occur in subsequent structures.
The recognition of faces in the human cerebral cortex seems to be mediated by a discrete region of the fusiform gyrus, but the function of this area is dependent on interactions with other cortical areas. Damage to the fusiform gyrus and to the area mediating face recognition can lead to prosopagnosia, and damage to the amygdala can lead to problems in social integration as characterised by the Kluver–Bucy syndrome. The role of the perception of disgust is less well known and less understood. However, people suffering from obsessive-compulsive disorder (OCD) also seem to suffer from an impairment of the perception of disgust (Sprengelmeyer et al., 1997). OCD seems to have its genesis in childhood, and it is possible that the failure to pick up social cues relating to items or activities that normally generate disgust may lead to the development of aberrant social behaviours, such as the washing or checking rituals observed in OCD. These results emphasise the importance of being able to process facially conveyed information correctly for a very social primate like humans, and the difficulties that can arise when things go wrong.
Summary of key points
(1)Damage to certain areas of the brain can cause a specific form of agnosia called prosopagnosia. This is the inability properly to process visual information on facial identity or facially conveyed information, such as expression or direction of gaze.
(2)In humans, the area of the brain which mediates face-recognition is the fusiform gyrus, and the region which mediates direction of attention, lip reading and biological motion is the superior temporal sulcus (STS).
(3)Face processing seems to show lateralisation. The right side of the human cortex seems to be specialised to process faces as a single pattern. The left side processes faces in a ‘piecemeal’ manner, that is, feature by feature rather than as a single pattern.
(4)Although recognition of faces or facial expression seems to occur in the fusiform gyrus and related areas, subsequent structures have an important influence on these processes. Of particular importance in the recognition of fear is the amygdala, whose normal functioning is necessary for the pattern of eye movement necessary for the detection of fear in a face.
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(5)The neural response to expressions of disgust is in the anterior insular. The insular has been identified as the gustatory cortex in primates and plays an important role in the appreciation of both tastes and odours. This suggests that the appreciation of visual stimuli depicting other’s disgust may be closely linked to the perception of potentially aversive stimuli.
(6)Another important area for the interpretation of emotion in the context of social interactions is a region of the ventromedial frontal cortex called the orbitofrontal cortex (OFC). Damage to this area, such as in the famous case of Phineas Gage, disrupts the interpretation of information relating to emotion and a subject’s ability to function socially.