Norman Geschwind

Human Brain: Left-Right Asymmetries in Temporal Speech Region

We have found marked anatomical asymmetries between tile upper surfaces of the human right and left temporal lobes. The planum temporale (the area behind Heschs gyrus) is larger on the left in 65 percent of brains; on the right it is larger in only 11 percent. The left planum is on the average one-third longer than the planum. This area makes up part of the temporal speech cortex, whose importance is well established on the basis of both anatomical findings in aphasic patients ans cortical stimulation at operation.

Limbic and sensory connections of the inferior parietal lobule (area PG) in the rhesus monkey: A study with a new method for horseradish peroxidase histochemistry

The caudal part of the inferior parietal lobule (area PG) was injected with horseradish peroxidase (HRP) in 6 hemispheres of 5 rhesus monkeys. The retrograde transport of HRP resulted in the labeling of neurons in diverse cortical and subcortical areas. In cortex, labeled neurons were noted in prefrontal cortex (areas 8, 45, 46), in the banks of the intraparietal and superior temporal sulci, in medial parietal cortex, in cingulate cortex, in the retrosplenial area, in area TF and the caudal portions of the parahippocampal region. Subcortical sites with labeled neurons included the necleus basalis of the substantia innominata, the claustrum, the pulvinar and intralaminar thalamic nuclei, the pretectal area, the nucleus locus coeruleus and the raphe nuclei. Although many of the labeled neurons were seen in layers IIIc and V, each cortical area had an individual laminar pattern of labeled neurons. In these experiments, a benzidine dihydrochloride (BDHC) method was used which yields a blue reaction-product at sites containing HRP. BDHC affords superior visibility of labeled neurons, and a significant improvement in sensitivity when compared to a diaminobenzidine procedure in matching series of sections. Additional sections were also stained with a method which allows the simultaneous demonstration of HRP (blue) and acetylcholinesterase (reddish-brown). These revealed that virtually all substantia innominata (nucleus basalis) neurons which project to area PG are also rich in the enzyme acetycholinesterase. These afferents of PG may be classified into sensory association, limbic and reticular categories. It is argued that this arrangement of afferent imput may afford a convergence of limbic and sensory information in area PG and that this may subserve a significant function in the process of sensory attention.

Dichotic Listening in Man After Section of Neocortical Commissures

Doreen Kimura’s modification of the dichotic listening technique of Broadbent for use as a means of studying the functions of the individual hemispheres represents a major contribution to the study of the human brain, since it is completely harmless and can be used in normals as well as patients. Mr. Robert Sparks and I made the first study of dichotic listening in a patient with a callosal section, whom we were able to study through the kindness of Dr. Joseph Bogen, Dr. Roger Sperry and Dr. Michael Gazzaniga. Our study was based on only one patient, and we were therefore pleased that a subsequent study of a larger series of callosally sectioned patients by Milner et at. (1968) confirmed our findings.

Isolation of the speech area

The credit for discovering this remarkable patient and for studying her so carefully over many years goes to Dr. Fred Quadfasel, who also demonstrated her remarkable capacity for verbal learning. Without these astute clinical and experimental observations the subsequent post-mortem findings would have been of little use. Combining the two, however, made it possible to draw far-reaching theoretical conclusions from this experiment of nature. Perhaps the most important conclusion is that comprehension of language is not unitary. Thus this patient could complete common phrases, and could perform other discriminatory activities, while she failed at others. This conclusion is reinforced by other findings, e.g., some patients with severe comprehension deficits for questions and commands for the individual limbs may yet respond very well to commands carried out with the axial musculature, e.g., ‘sit down’, ‘stand up’ ‘walk’, etc.

On the possible role of neocortex and its limbic connections in the process of attention and schizophrenia: clinical cases of inattention in man and experimental anatomy in monkey.

IN HIS authoritative and pioneering monograph, BLEULER~ pointed out that derangements of attention constitute a cardinal component of schizophrenia. Since then, numerous clinical and experimental investigations have concluded that a deficit in selective attention is, indeed, a salient characteristic of schizophrenic syndromes. However, such deficits are certainly not confined to schizophrenia. In fact, the clinical neurologist is often faced with cases where the most outstanding manifestation of the disease process is an inability of the patient to direct and maintain attention appropriately.? Consequently, in this article which may initially seem to depart from the common theme of this symposium, we will describe deficits of attention which the neurologist encounters in a non-schizophrenic population. With the help of these clinical observations and additional experimental neuroanatomical data, we will suggest that the cerebral regions subserving attention may be situated within the most advanced portions of “association” neocortex. Furthermore, we will demonstrate that these same neocortical regions have direct neuronal connections with those parts of the “limbic” brain which are implicated in the modulation of emotional and motivational behavior. Although such direct connections are at first glance surprising, on further study, their significance to the process of selective attention becomes clear. Since attentional and affective abnormalities also characterize schizophrenia, we will advance hypotheses to suggest how this clinical and experimental information may become relevant to current anatomical and pharmacological concepts pertaining to schizophrenia.

Gerstmann Syndrome without Aphasia

Summary A patient with Gerstmann syndrome without aphasia is presented, and it is suggested that the existence of such cases casts doubt on the contention that aphasia is the underlying mechanism of the syndrome. Some of the other recent attacks on the theoretical or practical importance of the Gerstmann syndrome are summarized and criticized. The patient presented here manifested other unusual features. Her disorder was a slowly progressive presenile deterioration, but with good preservation of memory. There was a distinct discrepancy in the degree of agraphia in the right and left hands and the possible mechanisms of this are discussed.

The ophthalmoplegic form of the Guillain-Barre-syndrome: an immunologic study.

The exact pathogenesis of the ophthalmoplegic form of the Guillain‐Barre syndrome is not understood. Detailed immunologic studies in a classical case of this entity showed cell‐mediated immunity to peripheral nerve antigens but not to central myelin antigens. It is concluded thas this syndrome is a true variant of Guillain‐Barre polyneuritis and that the lesions are peripheral and not central as often postulated.