Impairment of memory functions following acute head injury
Fodor, Iris Elaine Goldstein
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The goals of the present research were two fold: first to examine an acute head injury sample to test memory functions, second to study what parts of the memory process are most affected during post traumatic amnesia with special emphasis on retrieval of structured material in delayed recall. Subsidiary interests include studying recovery and the relationship between memory functioning and severity of injury. After head injury a common complaint is a transitory period of amnesia for recent events (PTA). PTA is often thought of as one stage in the recovery of consciousness and is believed to be an index of neurological severity. A model was proposed to account for amnesia. Two separate memory mechanisms prior to permanent storage were hypothesized, one for short term and the other for long term storage. Inputs are coded on the basis of recurrent patterns of common features. Retrieval occurs by means of the coded representation. Amnesia is viewed as a malfunctioning of the coding mechanism. Amnesia is thus held to be an inability to fully utilize coding of stimulus material as an aid in recall. Following this theory, it was predicted that the perceptive and cognitive functions were operating in amnesia and that immediate recall was also unimpaired. The major prediction was that retrieval of structured stimulus material by delayed recall would be impaired compared to normals, while retrieval of unrelated stimulus material would be unimpaired. Retrieval by recognition would only be mildly impaired because less information is required for recognition than for recall. Hence, the memory event can be reconstructed in recognition on the basis of partial coding. It was further predicted that, with recovery, there would be improvement of memory functioning and that there would be a relationship between severity of injury and memory functioning. A Memory Scale was constructed which included four subtests designed to test the above theory. Each subtest included both related and unrelated stimulus material. An additional test (a Picture Similarities Test) was employed to measure conceptualization. Forty seven acute head injury patients were tested as soon after injury as possible and matched with forty four control subjects (patients with acute trauma, but no head injury) on the basis of age, education, occupation and performance on the Ammons Picture Vocabulary Test. Head injury patients with approximately normal intelligence (Ammons I.Q. 80 or above) followed the predictions with these exceptions: Immediate recall and recognition of related stimulus material showed a trend toward impairment, though immediate recall and recognition of unrelated stimulus material did not. The findings with the patients with normal intelligence suggest, that while cognitive and perceptual abilities are not affected by trauma, utilization of organization as an aid in recall of related stimulus material is not as effective in the experimental· as in the control group. Head injury patients with low I.Q.'s (79 or below on the Ammons) demonstrated impairment of perception and immediate recall as well as the predicted impairment of delayed recall. These patients appeared to exhibit a generalized cognitive disturbance. No definite trends toward recovery were observed on any of the memory tests. There was also no relationship between severity of injury and performance on the Memory Scale. However, there was a significant correlation between performance on the Ammons and Picture Similarities tests and neurological severity. Patients with the lowest scores on these tests were most impaired neurologically. Intelligence thus appears to be more closely associated with severity of injury than is memory functioning per se.
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