Hypernatremic thirst deficiency and memory disorders following hypothalamic lesions

Verbal memory in brain damaged patients under different conditions of retrieval aids: a study of frontal, temporal, and diencephalic damaged subjects

The performance of 36 patients, divided into six groups, and 13 control subjects was investigated in paired-associate learning. The patients had right or left prefrontal, right or left anterior lateral temporopolar or medial temporal lobe damage, or lesions restricted to diencephalic areas. As tasks, two lists of paired words had to be learned, with the first list presenting only the word pairs, and the second one embedding the word pairs in sentences of a highly imaginable content. Recall consisted of immediate or delayed (48 hrs) free recall of the first list (condition I), of immediate or delayed recall of the second list (with visual imagery as a learning aid; condition II), and of cued recall (in which the sentence form was presented with a blank space where the word to be recalled had been previously; condition III). Control subjects clearly performed best under all conditions, manifesting a ceiling effect for the second and third ones under immediate recall. Among the brain-damaged groups the diencephalic subjects were poorest and gained only little from the aids given for learning and recall. Of the four patients with medial temporal lobe damage, those two with bilateral lesions were nearly as bad as the diencephalic lesioned subjects. The other patients were markedly inferior to the control subjects, but gained considerably under conditions II and III. These statements hold for immediate and delayed recall, though for the delayed recall conditions all groups showed a reduction in performance which amounted to roughly half of the values they had had under immediate recall. It is concluded that increasing the possibilities for depth of information processing assists brain damaged (as well as normal) subjects in verbal learning, but that the advantage of aiding them at the moment of encoding and retrieval is highest for patients with restricted lesions and/or with lesions not invading the two regions most regularly implicated in long-term information processing (the diencephalon and the medial temporal lobe area).

The neuropathology of amnesia

Relations between brain damage and memory disturbance are outlined with emphasis on the so-called amnesic syndrome. Following a brief introduction into forms of memory and memory failures, the basic causes of brain damaage (with relevance to amnestic failures) are described. Thereafter, the two best-known forms of brain damage-amnesia relations are reviewed: the consequences of damage to medial temporal lobe structures and to diencephalic regions. For the cases with medial temporal lobe damage, evidence is reported in greater detail for H.M., who has been examined more than any other amnesic patient for more than 30 years now, as a considerable amount of literature has accumulated on his behavior in diverse situations. Other cases with more or less circumscribed damage to medial temporal lobe structures are reviewed so as to outline criteria for or against the hypothesis that there are regions within the medial temporal lobe whose damage might be critical for the amnesic syndrome. Two cases of diencephalic amnesia are summarized in particular (cases of Mair et al., 1979) as they have received extensive neuropsychological and neuropathological investigation. Other cases with, for example, Korsakoff's disease are reviewed, as well as cases with diencephalic, or combined mesencephalic-diencephalic damage without nutritional causes. A third group of patients with massive, but still selective amnesic disturbances are then described: cases of basal forebrain damage, followed by descriptions of Alzheimer's disease which has similarities in the underlying neuropathology. This leads over to cases with more generalized intellectual deteriorations (dementia), which may have developed on the basis of primarily cortical damage or damage principally to basal ganglia structures. After reviewing cases with mainly material-specific memory failures--usually as a consequence of restricted neocortical damage--a separate section follows on patients in whom retrograde amnesia is the prominent symptom. The contribution of animal models of human amnesia is critically reviewed and discrepancies are analyzed between human and animal memory disturbances. This section emphasizes the value of investigating inter-dependencies between brain structures by pointing out that relations between memory disturbances and brain damage may be more complicated than apparent from a simple structure-function assignment. This aspect is further followed up in the conclusions.