Verbal memory impairment after right temporal lobe surgery: role of contralateral damage as revealed by 1H magnetic resonance spectroscopy and T2 relaxometry.

We assessed performance on selected tests of verbal memory in 48 patients who had undergone either anterior temporal lobectomy or selective amygdalo-hippocampectomy for the relief of pharmacologically intractable epilepsy. We related performance both to the side of surgical excision and to the presence or absence of abnormalities in the contralateral, unoperated, temporal lobe, as revealed by proton magnetic resonance spectroscopy (1H MRS) or T2 relaxometry. There were abnormalities on the unoperated side detected by 1H MRS in 50% of the 34 patients who successfully underwent spectroscopy, and by T2 relaxometry in 33% of the complete series of 48 patients. There was no systematic relationship between seizure outcome and the presence or absence of abnormalities on the unoperated side. Verbal memory deficits were present in patients with left-sided excision, regardless of whether there were abnormalities on the unoperated side. The patients with right-sided excision also had verbal memory deficits, but only in the group with magnetic resonance abnormalities on the contralateral (ie, left) side and only on delayed recall. The study extends previous findings on the role of the temporal lobes in memory and highlights the role of these new magnetic resonance techniques in relating cognitive processes to brain structures.

Strategic search and retrieval inhibition: the role of the frontal lobes.

Recall of words from categorised lists was examined in 77 patients and 12 normal control subjects. In Experiment 1, both left temporal-lobe excisions that included the hippocampus (LTH) and left frontal-lobe removals (LF) impaired free recall, but the LF group performed normally when encoding and retrieval strategies were supplied. In Experiment 2, experimentally induced interference during cued recall abnormally hampered performance for the LF, but not for the LTH group. Subsequent removal of the interfering cues resulted in improved performance for the LF group. Thus, the integrity of the left frontal lobe seems indispensable for normal strategic retrieval and for the suppression of potentially interfering items in verbal memory.

Memory for visuospatial location following selective hippocampal sclerosis: the use of different coordinate systems.

This study addressed the role of the medial temporal lobe regions and, more specifically, the contribution of the human hippocampus in memory for body-centered (egocentric) and environment-centered (allocentric) spatial location. Twenty-one patients with unilateral atrophy of the hippocampus secondary to long-standing epilepsy (left, n = 7; right, n = 14) and 15 normal control participants underwent 3 tasks measuring recall of egocentric or allocentric spatial location. Patients with left hippocampal sclerosis were consistently impaired in the allocentric conditions of all 3 tasks but not in the egocentric conditions. Patients with right hippocampal sclerosis were impaired to a lesser extent and in only 2 of the 3 tasks. It was concluded that hippocampal structures are crucial for allocentric, but not egocentric, spatial memory.

Topographical disorientation: selective impairment of locomotor space?

We report a single-case study of a patient who suddenly lost her ability to orient herself in her neighbourhood. On formal testing she demonstrated remarkably selective deficits in episodic and semantic memory of topographical items and rouse. Her general intellectual abilities were unaffected as were basic perceptual processes and episodic and semantic memory other than topography. We interpret her deficit as a further example of category-specific processing impairment affecting knowledge acquired through selective channels-in this case visuo-locomotor information.