David M. Bear’s research while affiliated with Harvard Medical School and other places

Students of artificial intelligence often focus on processes involved in solving highly abstract problems: synthesizing a chemical structure from given precursors, optimizing the design of an electrical circuit, or constructing a winning chess strategy. These problems are of obvious interest to the human mind-and brain-and yet we cannot say that our lives depend directly on their solution!

Discoveries in neurology and linguistics indicate that many aspects of human language are determined by specific structural features of the brain, a notion which differs radically from the more prevalent idea of language being an arbitrary, culturally evolved set of symbols and combinatorial rules which during development somehow become represented upon an infinitely malleable nervous system. The present study has attempted to examine whether such neurological specification might extend to other aspects of our social interactions as well, particularly the communication of affect through paralinguistic cues. But before describing the rationale for our own studies, it might be best to mention a little more about spoken language.

Subjects sustaining right hemisphere damage were impaired in the ability to evaluate emotional situations presented through nonverbal means, particularly through facial expressions. Left brain damage, even of considerable extent, led to significantly milder deficits. In agreement with these findings, a study in split-brain patients showed the isolated right hemisphere to be competent in evaluating facial expressions but less sensitive to body movements, while the left hemisphere showed the opposite pattern.

The regulation of such biologic drives as sex and aggression is a critical evolutionary function required of the nervous system. There is evidence that, in humans, the right hemisphere is dominant for many "emotional" functions. In the cortical regions involved in emotion, there are two important, complementary, sensorilimbic connective pathways: a dorsal system critical for surveillance, attention, and arousal and a ventral system specialized for stimulus identification, learning, and emotional response. Hemispheric specialization may introduce lateral asymmetries in these sensorilimbic connections, which could account for contrasting dominance in both emotional functions and some cognitive domains.

Assessments of mood disturbance and "vegetative" (appetite or sleep) disturbance as well as a single-dose dexamethasone suppression test (DST) were carried out in 25 randomly selected stroke patients and in 13 nonstroke control patients hospitalized in a rehabilitation center. Prevalence rates of moderate-to-serve depression of mood and vegetative disturbance were significantly higher in stroke patients than controls (48% and 52% versus 0% and 8%, respectively), as was the prevalence of abnormal DST results (52% versus 8%). Abnormal DST results were associated with the occurrence of moderate to severe mood, appetite, and sleep disturbances among all patients. in 2 stroke patients, repeated DST results paralleled the clinical course. The DST may be useful as an adjunct to the diagnosis and in monitoring the progress of the common and potentially reversible mood and vegetative disturbances occurring after stroke.

Temporal lobe epileptics undergoing psychiatric hospitalisation were contrasted with patients suffering idiopathic psychiatric syndromes or other epilepsies. Quantitative ratings from blind interviews conducted according to a protocol confirmed the appearance of a statistically distinctive behavioural profile, including the desire for social affiliation, circumstantiality, religious and philosophic interests, and deepened affects, among the temporal lobe epileptics.

Psychological changes in patients with temporal lobe epilepsy are considered. Prior observations of correlated psychiatric diagnoses and objections to these are reviewed. Specific features of behavior and thought, derived from the literature and clinical experience, are suggested as a more effective way of characterizing the interictal syndrome; their accuracy is supported by quantitative results of an ongoing study, Enhanced affective association is proposed as a mechanism underlying these diverse features. This is interpreted in the light of theoretical and experimental accounts that anatomical connection between sensory and limbic structures are established within the temporal lobe. In contrast to sensory limbic disconnection which results in dissociation of stimuli from affective values, it is suggested that the epileptic process effects sensory limbic hyperconnection, leading to a suffusion of experience with emotional coloration.

From a clinical perspective, alterations in the emotions or behavior of an individual primarily present a problem in differential diagnosis. For this reason, a simple rule or generalization has long been sought to distinguish behavioral syndromes of organic causation from functional—idiopathic or learned—psychiatric disorders.

• Patients with unilateral temporal epileptic foci were contrasted with normal subjects and patients with neuromuscular disorders in the evaluation of specific psychosocial aspects of behavior. Eighteen traits were assessed in equivalent questionnaires completed by both subjects and observers. The epileptic patients self-reported a distinctive profile of humorless sobriety, dependence, and obsessionalism; raters discriminated temporal lobe epileptics on the basis of circumstantiality, philosophical interests, and anger. The right temporal epileptic displayed emotional tendencies in contrast to ideational traits of left temporal epileptic. Right temporal epileptics exhibited "denial," while left temporal epileptics demonstrated a "catastrophic" overemphasis of dissocial behavior. The results support the hypotheses that sensory-affective associations are established within the temporal lobes, and that, in man, there exists a hemispheric asymmetry in the expression of affect.