Dennis D. Spencer

Verbal memory impairment correlates with hippocampal pyramidal cell density

Thirty-five patients with medically refractory epilepsy localized to the temporal lobe (18 left, 17 right) completed the verbal Selective Reminding Test before surgery. Verbal memory impairments existed before surgery regardless of the lateralization of the seizure focus, but patients with left temporal seizure foci were significantly more impaired. After surgical removal of the mesial temporal lobe structures, 2 blinded observers established volumetric cell densities for hippocampal subfields CA1, CA2, CA3, the hilar area, and the granule cell layer of the area dentata. Statistically significant correlations existed between presurgical memory impairment and cell counts (in CA3 and the hilar area, only) for patients with left temporal seizure foci. These findings support the hippocampal model of memory and complement prior research documenting the memory impairments present after surgical removal of the mesial temporal structures.

Corpus callosotomy for epilepsy.: I. Seizure effects

Twenty-two patients were analyzed 2 or more years after corpus callosum section (9 partial, 13 total). Forty-one percent had class 1 outcome (elimination of secondarily generalized and complex partial seizures), 32% had class 2 outcome (elimination of secondarily generalized seizures), and 27% had class 3 outcome (no appreciable change). Total section was twice as effective in abolishing secondarily generalized seizures as was partial section (77% versus 35%). Statistically significant associations were seen between focal CT lesions and class 1 outcome, and between IQ less than 45 and class 2 or 3 outcome.

Electrophysiological studies of color processing in human visual cortex.

Electrophysiological recordings from human visual cortex were carried out with electrodes chronically implanted in 13 patients for localization of an epileptogenic focus. Visual evoked potentials (VEPs) elicited by red or blue checkerboard stimuli were recorded using an adaptation stimulus-test stimulus design in which color was the most salient feature. A significant color effect, defined as a statistically significant effect of the adaptation stimulus on test stimulus VEPs evoked by the same or a different color, was determined for various cortical regions: medial lingual gyrus, 20%; lateral lingual gyrus, 38%; posterior fusiform gyrus, 50%; anterior fusiform gyrus, 0%; inferior temporal gyrus, 5%; occipital pole, 30%; lateral surface of non-visual cortex, 6%; inferior parietal and temporal cortex, 5%. The time course of the significant color effects suggests that wave length-selective neuronal activity occurs initially at the first stage of cortical processing in the medial lingual gyrus, followed by progressively later activation of the lateral lingual gyrus, the posterior fusiform gyrus, and the inferior temporal gyrus. In two patients, stimulation of the lateral lingual and fusiform gyri elicited color sensations in the contralateral half-field, whereas stimulation of the medial lingual and cuneate gyri evoked retinotopically appropriate quadrantic shimmering devoid of color. These results suggest that a region of inferior occipital cortex, primarily the posterior portion of the fusiform gyrus, is involved in color perception and may be homologous with area V4 in monkeys. There is also a region of dorsolateral surface cortex which exhibits a fairly high percentage of significant color effects and when stimulated may evoke sensations of color. This region may be the same as the dorsolateral region thought to be involved in selective attention to color.

Corpus callosotomy for epilepsy. II. Neurologic and neuropsychological outcome.

Eighteen uncontrolled epileptic patients had neuropsychological evaluation before and after partial or total corpus callosotomy. In patients with early-onset seizures and signs of severe unilateral CNS dysfunction, callosotomy produced no deficits and several improvements. AH patients whose language-dominant hemisphere did not control their dominant hand had impairments in some aspect of speech and language function after callosotomy. In some patients, unilateral deterioration of motor function was observed, and was associated with mild to moderate dysfunction in the contralateral hemisphere (ie, memory impairment or preexisting hemiparesis). Postoperative deficits occurred with partial, as well as total, section.

Verbal memory impairment resulting from hippocampal neuron loss among epileptic patients with structural lesions

We recently demonstrated statistically significant correlations between presurgical memory impairment and hippocampal volumetric cell densities (in CA3 and the hilar area only) for patients with idiopathic left temporal lobe epilepsy who exhibited marked hippocampal neuron loss.In the present research we determine whether the same relationship exists for patients with structural lesions, in whom hippocampal neuron loss was minimal. Rank-order correlations of verbal memory test results (ie, Long Term Retrieval score of the verbal Selective Reminding Test, Percent Retention index of the Logical Memory subtest of the Wechsler Memory Scale) and hippocampal volumetric cell densities (subfields CA1, CA2, CA3, the hilar area, and the granule layer of area dentata) were computed for 22 patients with structural lesions and medically refractory epilepsy of temporal lobe onset (11 left, 11 right). There were statistically significant correlations between Long Term Retrieval and the volumetric cell density of CA1 (r equals 0.62, p less than 0.05) and between percent retention and the volumetric cell density of CA2 (r equals 0.60, p less than 0.05) for patients with left hemisphere lesions. No other correlations were found for patients with left or right temporal lobe lesions. NEUROLOGY 1995;45: 2154-2158