Disorders of Social Conduct Following Damage to Prefrontal Cortices

Hanna Damasio1

Some of the most important human values pertain directly to social conduct, and it is apparent that the study of disorders of social conduct from a neurological perspective can yield important information regarding the neurobiology of human values. My purpose in this chapter is to review the evidence I regard as most relevant in this area.

Although it is manifestly difficult to define "normal" social conduct, most readers would agree on what generally constitutes good or bad social conduct. I will assume that agreement and simply say that normal social conduct is that which respects 1) the social conventions of a given culture, and 2) the ethical rules and laws of that culture.

I also assume that most readers expect normal social conduct to result not only from the acquisition of socio-cultural knowledge and skills, but also from biological (and especially neurobiological) factors. In fact, I suspect most believe that an interaction of socio-cultural and biological factors is necessary for normal social conduct to emerge, and would agree that in order for normal social conduct to occur, certain conditions have to be met: 1) the biological devices necessary for the behavior must have been put in place by the genome; 2) the current environment must be compatible with the behavior; 3) the current biological state of the individual's organism must be such that the biological devices are operational; and 4) the past environment must have allowed the individual to develop biologically and psychologically in such a way that the relation between the behavior and the social situation could be properly adjusted.

Once these assumptions are agreed upon, the question I would like to pose is as follows: what do we know about the biological devices necessary for normal social conduct to occur?

A first line of evidence that helps answer this question comes from lesion studies in neurological patients. Here I will present results from the investigation of a large group of patients who have had a neurological event that damaged their frontal lobes. In some, the damage occurs in adulthood; more rarely, it can also occur in childhood. The critical event is often the resection of a brain tumor (e.g., a meningeoma) but can be a cerebrovascular accident (e.g., a ruptured anterior communicating aneurism; a stroke in the territory of the anterior cerebral artery) or even head trauma. The principal damage centers on the ventral and mesial sectors of the prefrontal cortices (Fig. 1).

1 University of Iowa College of Medicine, Department Neurology, Iowa City IA 52242, USA; e-mail: [email protected]

Fig. 1. Three-dimensional reconstruction, from high resolution MR scans, of 3 subjects, fully right-handed, with adult-onset ventro-medial prefrontal damage. In A the damage is bilateral, the result of resection of a meningeoma, in a 54 year old woman; in B the damage only involves the right ventro-medial prefrontal region and results from an infarct in the territory of the anterior cerebral artery, in a 61 year old man; and in C the damage is limited to the left anterior and medial ventral prefrontal region, the result of resection of a cystic lesion in a 32 year old woman.

Fig. 1. Three-dimensional reconstruction, from high resolution MR scans, of 3 subjects, fully right-handed, with adult-onset ventro-medial prefrontal damage. In A the damage is bilateral, the result of resection of a meningeoma, in a 54 year old woman; in B the damage only involves the right ventro-medial prefrontal region and results from an infarct in the territory of the anterior cerebral artery, in a 61 year old man; and in C the damage is limited to the left anterior and medial ventral prefrontal region, the result of resection of a cystic lesion in a 32 year old woman.

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