Unilateral medial temporal lobe memory impairment: type deficit, function deficit, or both?

• Published in: Neuropsychologia 1998-02, Vol.36 (2), p.115-127
• Main Authors: Dobbins, Ian G, Kroll, Neal E.A, Tulving, Endel, Knight, Robert T, Gazzaniga, Michael S
• Format: Article
• Language: English
• Subjects: Adult; Adult and adolescent clinical studies; Aged; Biological and medical sciences; Cerebrovascular Disorders - physiopathology; Cerebrovascular Disorders - psychology; commissurotomy; Corpus Callosum - physiology; Disorders of higher nervous function. Focal brain diseases. Central vestibular syndrome and deafness. Brain stem syndromes; episodic memory; Female; Functional Laterality - physiology; Hippocampus - injuries; Hippocampus - physiopathology; Humans; Magnetic Resonance Imaging; Male; material specific; medial temporal lobe; Medical sciences; Memory Disorders - pathology; Memory Disorders - physiopathology; Memory Disorders - psychology; Mental Recall - physiology; Middle Aged; Nervous system (semeiology, syndromes); Neurology; Organic mental disorders. Neuropsychology; Psychology. Psychoanalysis. Psychiatry; Psychomotor Performance; Psychopathology. Psychiatry; task demands; Temporal Lobe - pathology; Temporal Lobe - physiopathology; verbal recall
• ISSN: 0028-3932; 1873-3514
• DOI: 10.1016/S0028-3932(97)00094-8

Previous research has characterized memory deficits resulting from unilateral hippocampal system damage as ‘material specific’, suggesting that left damage results in verbal memory impairment with preservation of visuospatial function and the converse with right damage. Implicit within this hypothesis are the assumptions that the systems are independent and memory is lateralized for each type of material. To test the verbal component of this hypothesis, unilateral hippocampal lesion and commissurotomy patients were compared with controls on a multiple-list free-recall task. The material specific hypothesis predicts severe impairment only with left lesions; right lesions and commissurotomy patients should be only minimally impaired. However, secondary memory was compromised at immediate recall for all patient groups, with both unilateral groups showing comparable and severe verbal episodic memory deficits. Final testing across all lists also revealed severe impairment in commissurotomy patients. Finding both unilateral groups to be similarly impaired for verbal material is taken as evidence against a material specific deficit during this verbal episodic memory task. Although previous data suggest that left patients are considerably more impaired during some verbal tasks, this may not be specific to the material, but rather the combination of material and task demands. Implications for the material specific hypothesis are discussed.