Alexithymia: an experimental study of cerebral commissurotomy patients and normal control subjects.

This study assessed alexithymia in six patients with complete cerebral commissurotomy, two patients with partial commissurotomy, and eight matched control subjects. Comparisons were based on content-analytic measures of the subjects' spoken and written responses to a film that symbolically represented death and loss. The commissurotomized patients were more alexithymic on all four lexical-level variables, all six sentential-level variables, and all six global-level variables. Discriminant function analysis found a linear combination of four variables that effectively discriminated groups of fully commissurotomized, partially commissurotomized, and normal control subjects and correctly classified 15 of the 16 subjects.

Completeness of callosotomy shown by magnetic resonance imaging in the long term.

Six individuals who had complete cerebral commissurotomy for medically intractable epilepsy participated in a magnetic resonance imaging study 20 or more years postoperatively. In all cases the completeness of callosotomy was clearly demonstrable. The status of the anterior commissure, cut in all six, could not be confirmed with the same confidence.

My developing understanding of Roger Wolcott Sperry's philosophy.

Reviewed are some of the dramatic experimental results and penetrating analyses characterizing the career of Roger Sperry. These require that we seriously consider his opinions regarding matters not yet testable, especially regarding the brain/mind relationships. His opinions include first, that a worthwhile understanding of brain function requires a biological explanation of consciousness; second, that mental properties described by him as "overall pattern effects in brain dynamics" can govern neuronal traffic at the cellular level by virtue of "mental forces'; and third, that further development of this outlook can provide a scientific basis for moral values. Discussion here is restricted to the first two of these points, urging that most criticisms of them arise largely from semantic confusions inherited from our past. Particular emphasis is placed on distinguishing mind from soul, thus totally separating the brain-onto-mind mapping problem from the nexus problem inherited from Descartes. Taken here is a physicalist position regarding mind, together with agnosticism regarding the nonmaterial.

Creativity and the corpus callosum.

A duality of mind is readily demonstrable in split-brain humans, and evidence is steadily accumulating that ongoing interhemispheric communication is incomplete in the intact brain. It is now certain that the corpus callosum can transfer high-level information from one hemisphere to another. When we take into account the well-established principle of hemispheric specialization, added to the impressive normality of split-brain humans in ordinary social situations, a physiologic explanation for at least some forms of creativity seems close at hand. What is required is a partial (and transiently reversible) hemispheric independence during which lateralized cognition can occur and is responsible for the dissociation of preparation from incubation. A momentary suspension of this partial independence could account for the illumination that precedes subsequent deliberate verification. From this point of view, we can understand better the opinion of Frederic Bremer, who wrote years ago that the corpus callosum subserves "the highest and most elaborate activities of the brain"--in a word, creativity.

Alexithymia and the split brain: VI. Electroencephalographic correlates of alexithymia.

Electroencephalographic recordings of eight corpus callosotomy patients and eight precision-matched control subjects were obtained as subjects watched a film symbolically depicting death. A content-analytic measure of alexithymia was regressed on eight auto-spectral alpha-band intensity averages and on subsets of alpha-band coherence averages. Results were interpreted on the basis of three possible mechanisms of alexithymia: (1) Alexithymic subjects had more right-temporal alpha-band intensity, suggesting inadequate understanding of the film. (2) A possible lack of inner speech in alexithymics was suggested by their relative alpha abundance of the left frontal and left temporal channels but left parietal alpha desynchronization, and by their lower left frontotemporal but higher left parietofrontal and left parietotemporal coherences. (3) Alexithymic subjects had higher right frontal-left parietal and left frontal-left parietal coherences, suggesting possible interhemispheric inhibition of expression. Expressive subjects had higher right frontal-left temporal (and homologous interhemispheric frontal, parietal, and frontal) coherences, suggesting interhemispheric facilitation of verbal expression.

Perception of dichotic chords by normal and commisurotomized human subjects.

A perceptual suppression of an ipsilateral by a concurrent contralateral auditory signal occurs in commissurotomized subjects and probably in normal subjects. This suppression of the ipsilateral signal depends on the nature of the auditory stimuli. For dichotic speech sounds the suppression of the ipsilateral signal is overwhelming; for dichotically presented pure tones it is not present. For dichotically presented pure tones, unlike speech signals, a subcortical central pitch processor determines the contribution to the perceptual experience of the right and left ear signals in both normal as well as commissurotomized subjects.

Are unilateral right posterior cerebral lesions sufficient to cause prosopagnosia? Clinical and radiological findings in six additional patients.

Controversy has arisen regarding the neuropathological basis of prosopagnosia. Some investigators suggest that bilateral lesions are needed to cause the deficit, whereas others felt that a unilateral right posterior lesion is sufficient. Six patients with prosopagnosia with clinical and radiological evidence of unilateral right posterior lesions are presented. Our observations together with evidence from similar cases described in the literature suggest that an appropriately placed right hemispheric lesion may be sufficient to produce prosopagnosia.

Does cognition in the disconnected right hemisphere require right hemisphere possession of language?

It has been asserted at times that the human right hemisphere is cognitively inferior to that of a chimpanzee or even a monkey. Related is the even stronger claim that human consciousness, as well as cognition, requires language. These claims are discussed, and counterexamples are presented from both split-brain subjects and patients hemispherectomized in adulthood after customary development as righthanders.

A case report of pathological rule-governed syllable intrusion.

A detailed analysis of a unique speech disturbance, marked by the frequent appearance in the speech stream of a meaningless intrusive syllable, is presented. Following a lengthy thoracic surgery, an American English speaking patient began to speak with non-English prosodic patterns, which evolved to a conspicuous intrusion in his speech of the syllable /sis/. This syllable and its variants were attached to words in a manner which conformed to the regular phonological rules in English (for formation of plural, possessive, and third person singular morphemes). The distribution and frequency of the intrusive syllable are described, and possible explanations for the abnormal occurrence of this particular syllable are discussed.

Split-brain basics: relevance for the concept of one's other mind.

Frontal and horizontal sections of the cerebrum make plain that with a few exceptions (pineal, pituitary) all structures are paired. Hemicerebrectomy has made clear that only one member of the hemispheric pair suffices to sustain the sentiments, emotions, memories, and intentions both conscious and unconscious that we call in the aggregate, mind. That the anatomical duality can sustain a duality of mentation is evident from not only the split-brain results in all species examined but also the results of appropriate testing of anatomically intact individuals. There is no physiological evidence for a plurality of mind beyond duality. Psychoanalytic views of mind can benefit from revision in the light of the split-brain studies. But such revisions seem slight compared with improvements needed in the views prevalent among most other psychologic and philosophic theorists.

On the neurophysiology of consciousness: Part II. Constraining the semantic problem.

The main idea in this series of essays is that subjective awareness (more precisely, what I call C) depends upon the intralaminar nuclei of each thalamus (hereafter, ILN). This implies that the internal structure and external relations of ILN make subjective awareness possible. An array of material relevant to this proposal was briefly reviewed in Part I (Bogen, 1995). This Part II considers in more detail some semantic aspects and a bit of philosophic background as these pertain to propositions 0, 1, and 2 of Part I. Part II should be read in conjunction with Part I.

Some neurophysiologic aspects of consciousness.

An anatomico-physiologic approach to consciousness is facilitated by recognizing that the various meanings of consciousness have in common a crucial core C variously called subjectivity, awareness, consciousness-as-such, or consciousness per se. A sharp distinction is made between the property C and the contents of consciousness, partial loss of which is typical of cerebro-cortical lesions. The neuronal mechanism producing subjectivity also acts as an attention-action coordinator, hence must have specific connectivity requirements. These requirements are best met by the thalamic intralaminar nuclei (ILN). Whereas large lesions elsewhere leave C undisturbed, quite small bilateral lesions in ILN engender immediate unresponsiveness. This combination of anatomic and neurologic evidence is bolstered by a variety of physiologic evidence leading to the conclusion that further investigations of the ILN, and their interaction with lower centers as well as cerebral cortex, are most apt to yield a better understanding of consciousness.