Callosotomy Patients Research Articles

Alexithymia and the Split Brain: VI.: Electroencephalograplhic 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.

Validation of the lateral limits technique with a callosotomy patient

The lateral limits technique, presented by Myers and Sperry, was evaluated with a right- handed callosotomy patient. Consistent with traditional tachistoscopic findings, right visual-field presentations were superior for naming of letters and pictures, as well as rhyming. Left field presentations were superior for line orientation. Determination of the testing fields was insufficiently precise when the blind spot was used as a reference. An eye asymmetry was observed in both location of lateral limits and visual acuity. However, complete lateralization of input without interhemispheric transfer was achieved when presentation was made to fields of equal acuity. We conclude that the technique is valid and valuable for prolonged unilateral stimulation, but that care must be taken in determining appropriate and comparable testing fields.

Magnetic resonance imaging after corpus callosotomy.

Magnetic resonance imaging (MRI) can visualize the extent of corpus callosotomy performed for medically intractable epilepsy not amenable to focal surgery. Five patients underwent complete callosotomy and one an anterior callosotomy, aged 19 to 24 years, 21 to 53 months (prior to scanning). T1 images showed complete absence of the callosal shadow in five cases and visualization of the genu and splenium in the sixth case. T2-weighted pulse sequence spin-echo MRI showed intense image throughout the region of the entire callosum in the two cases with the longest postoperative course. The two middle cases showed intense T2 signal from the splenium, and the two latest showed no increase in T2 signal. We believe the increase in T2 signal in the transected callosum may represent an in vivo example of anisomorphic gliosis. T1 images demonstrate the anatomic extent of transection, while T2 images demonstrate the chemical and pathophysiologic sequence of transection. Thus, MRI is the imaging test of choice to evaluate callosotomy patients.

Contralateral and ipsilateral control of fingers following callosotomy

The extent of ipsilateral control of the distal limbs is not documented. In this experiment visuo-motor control of fingers was investigated in two callosotomy patients. A substantial amount of ipsilateral control was evident, especially for the left hand fingers. Ipsilateral control of the right hand was evident for the thumb and index fingers, but not for the other fingers. Left hand fingers did not vary significantly in degree of ipsilateral control.

Unimanual tactile anomia consequent to corpus callosotomy: Reduction of anomic deficit under hypnosis

Unimanual tactile anomia for objects palpated with the left-hand was studied in a 28-year-old callosotomy patient. Previous assessment of this patient Larrabee et al., [9]) and two currently reported assessments without inducing hypnosis showed marked anomic deficit. A series of assessments conducted under hypnosis showed substantially improved naming ability, especially in hypnotic sessions suggesting that the patient did not feel like speaking and that speaking was difficult. Among the possible mediators of this reduction of anomic impairment one can suggest factors such as motivational and attentional enhancements, suppression of left hemisphere interference, and even right hemisphere speech facilitation under hypnosis. These and other results also suggest that an hypothesized right hemisphere dominance during hypnosis may be accurate and possibly more obvious in callosotomy patients than in normal persons.

Typical cerebral hemisphere disconnection deficits following corpus callosum section despite sparing of the anterior commissure

Cerebral corpus callosum section is possibly as therapeutically effective as multiple cerebral commissurotomy while, according to the report of Risse et al. ( Neuropsychologia 16, 23–31, 1978), allowing a substantially greater retention of the important adaptive function of inter-hemispheric exchange of information. We report results of visual, auditory and tactile tasks administered to three callosotomy patients. Results show typical “split-brain” deficits, in each modality. These results suggest that the anterior commissure is not an affective commissure in the transfer of stimulation effects over the follow-up period studied.