Suzanne Corkin

Further analysis of the hippocampal amnesic syndrome: 14-year follow-up study of H.M. ☆

Abstract The report attempts to delineate certain residual learning capacities of H.M., a young man who became amnesic in 1953 following a bilateral removal in the hippocampal zone. In addition to being able to acquire new motor skills (C ORKIN [2]), this patient shows some evidence of perceptual learning. He also achieves some retention of very simple visual and tactual mazes in which the sequence of required turns is short enough to fit into his immediate memory span; even then, the rate of acquisition is extremely slow. These vestigial abilies, which have their occasional parallels in the patients everyday life, are assessed against the background of his continuing profound amnesia for most on-going events, an amnesia that persists in spite of above-average intelligence and superior performance on many perceptual tasks.

A neural dissociation within language: Evidence that the mental dictionary is part of declarative memory, and that grammatical rules are processed by the procedural system

Language comprises a lexicon for storing words and a grammar for generating rule-governed forms. Evidence is presented that the lexicon is part of a temporal-parietalhnedial-temporal declarative memory system and that granlmatical rules are processed by a frontamasal-ganglia procedural system. Patients produced past tenses of regular and novel verbs (looked and plagged), which require an -ed-suffixation rule, and irregular verbs (dug), which are retrieved from memory. Word-finding difficulties in posterior aphasia, and the general declarative memory impairment in Alzheimers disease, led to more errors with irregular than regular and novel verbs. Grammatical difficulties in anterior aphasia, and the general impairment of procedures in Parkinsons disease, led to the opposite pattern. In contrast to the Parkinsons patients, who showed sup pressed motor activity and rule use, Huntingtons disease patients showed excess motor activity and rule use, underscoring a role for the basal ganglia in grammatical processing.

Age-related alterations in white matter microstructure measured by diffusion tensor imaging

Cerebral white matter (WM) undergoes various degenerative changes with normal aging, including decreases in myelin density and alterations in myelin structure. We acquired whole-head, high-resolution diffusion tensor images (DTI) in 38 participants across the adult age span. Maps of fractional anisotropy (FA), a measure of WM microstructure, were calculated for each participant to determine whether particular fiber systems of the brain are preferentially vulnerable to WM degeneration. Regional FA measures were estimated from nine regions of interest in each hemisphere and from the genu and splenium of the corpus callosum (CC). The results showed significant age-related decline in FA in frontal WM, the posterior limb of the internal capsule (PLIC), and the genu of the CC. In contrast, temporal and posterior WM was relatively preserved. These findings suggest that WM alterations are variable throughout the brain and that particular fiber populations within prefrontal region and PLIC are most vulnerable to age-related degeneration.

Memory enhancement for emotional words: are emotional words more vividly remembered than neutral words?

Individuals are more likely to remember negative information than neutral information. In the experiments reported here, we examined whether individuals were also more likely to remember details of the presentation of negative words, as compared with neutral words. In Experiment 1, the remember-know procedure was used to examine the effect of emotion on the vividness of an individual’s memory, showing thatremember responses were more frequently assigned to negative words than neutral words. In Experiment 2, a source memory paradigm was used, and again, evidence that individuals’ memories were more detailed for negative than for neutral words was found. In Experiments 3–6, we examined the relative contribution of valence and arousal, finding that both dimensions increased the vividness of remembered information (i.e., items with valence only and those that elicited arousal were better remembered than neutral information) but that the effect was greater for words that evoked arousal than for those with valence only. The results support a qualitative, as well as a quantitative, memory benefit for emotional, as compared with neutral, words.

ACQUISITION OF MOTOR SKILL AFTER BILATERAL MEDIAL TEMPORAL-LOBE EXCISION

Abstract The acquisition of selected motor skills was studied in a 40-year-old man with a severe amnestic syndrome resulting from a bilateral medial temporal-lobe resection carried out 13 years before. On Rotary Pursuit, Bimanual Tracking, and Tapping, his scores improved from session to session, and on the one task where it was feasible to retest several days after the end of training (Rotary Pursuit), he showed complete retention. These results imply that motor learning can be mediated by brain structures still intact in this patient. The additional finding that he was inferior to normal men of his age on two tasks, in both initial and final levels of performance, is attributed to his relatively long reaction time rather than to the memory deficit.

What's new with the amnesic patient H.M.?

H.M. became amnesic in 1953. Since that time, nearly 100 investigators, first at the Montreal Neurological Institute and since 1966 at the Massachusetts Institute of Technology, have participated in studying him. We all understand the rare opportunity we have had to work with him, and we are grateful for his dedication to research. He has taught us a great deal about the cognitive and neural organization of memory. We are in his debt.

Semantic impairment and anomia in Alzheimer's disease

Impairment in naming visually presented objects was investigated in patients with a clinical diagnosis of Alzheimers disease. Impaired object naming correlated with difficulty listing the names of objects from a specified semantic category and with erroneous selection of words semantically related to the correct names for objects in a name recognition test. These results suggest that patients with Alzheimers disease have a semantic impairment characterized by inability to distinguish among objects that are members of the same semantic category, and that this impairment is associated with difficulty producing the names for objects. Semantic impairment was present in patients with normal ability to discriminate visually presented shapes, indicating that the semantic deficit in Alzheimers disease occurs independently of abnormalities of visuospatial function. Patients tended to make errors on the same items in both confrontation naming and name recognition tests, suggesting that the semantic impairment in Alzheimers disease involves loss of information about specific objects and their names.

Evidence for a dissociation between perceptual and conceptual priming in Alzheimer's disease

The status of perceptual priming and word-completion priming in patients with Alzheimers disease (AD) was examined. Experiment 1 established the reliability of the perceptual priming measure in normal subjects. In Experiment 2, AD patients showed a normal magnitude of perceptual priming. In Experiment 3, a single group of AD patients showed a normal magnitude of perceptual priming and impaired word-completion priming. Further, word-completion priming, but not perceptual priming, was correlated with verbal fluency performance in AD. These results suggest a dissociation between two components of verbal priming. Perceptual priming may reflect the operation of a structural-perceptual memory system mediated by occipital lobe regions relatively spared in AD. Word-completion priming may reflect the operation of a lexical-semantic memory system mediated by temporoparietal lobe regions compromised in AD.

Age-Related Changes in Prefrontal White Matter Measured by Diffusion Tensor Imaging

Age‐related degeneration of brain white matter (WM) has received a great deal of attention, with recent studies demonstrating that such changes are correlated with cognitive decline and increased risk for the development of age‐related neurodegenerative disease. Past studies have used magnetic resonance imaging (MRI) to measure the volume of normal and abnormal tissue signal as an index of tissue pathology. More recently, diffusion tensor MRI (DTI) has been employed to obtain regional measures of tissue microstructure, such as fractional anisotropy (FA), providing better spatial resolution and potentially more sensitive metrics of tissue damage than traditional volumetric measures. We used DTI to examine the regional basis of age‐related alterations in prefrontal WM. As expected from prior volumetric and DTI studies, prefrontal FA was reduced in older adults (OA) compared to young adults (YA). Although WM volume has been reported to be relatively preserved until late aging, FA was significantly reduced by middle age. Much of prefrontal WM showed reduced FA with increasing age. Ventromedial and deep prefrontal regions showed a somewhat greater reduction compared to other prefrontal areas. Prefrontal WM anisotropy correlated with prefrontal WM volume, but the correlation was significant only when the analysis was limited to participants over age 40. This evidence of widespread and regionally accelerated alterations in prefrontal WM with aging illustrates FAs potential as a microstructural index of volumetric measures.

The impaired learning of semantic knowledge following bilateral medial temporal-lobe resection.

The integrity of several aspects of semantic memory (including knowledge of the meaning, lexical status, perception, and pronunciation of words and famous names) was examined in H.M., a patient with anterograde amnesia following bilateral medial temporal-lobe excision. Despite normal memory for such semantic knowledge acquired prior to the onset of his amnesia in 1953, H.M. showed a severe deficit in memory for semantic information encountered subsequently. In combination with the previously reported impairments in new learning shown by H.M., the deficits observed here point to an association between semantic and episodic memory, and do not lend support to a distinction between them. The acquisition of semantic and episodic information, therefore, appears to depend upon a common memory system that requires the intact functioning of medial temporal-lobe structures.