Medial temporal lobe amnesia: Gradual acquisition of factual information by nondeclarative memory - PubMed (original) (raw)
Case Reports
Medial temporal lobe amnesia: Gradual acquisition of factual information by nondeclarative memory
Peter J Bayley et al. J Neurosci. 2002.
Abstract
Most amnesic patients with damage to the medial temporal lobe retain some capacity to learn new information about facts and events. In many cases, the learning appears to depend on a residual ability to acquire conscious (declarative) knowledge. We have studied the capacity for semantic (fact) learning in the profoundly amnesic patient E.P., who has extensive damage limited primarily to the medial temporal lobe. E.P. was presented with factual information (novel three-word sentences) during 24 study sessions across 12 weeks. E.P. performed much more poorly than controls but demonstrated unmistakable improvement across the sessions, achieving after 12 weeks a score of 18.8% correct on a cued-recall test and 64.6% correct on a two-alternative, forced-choice test. Unlike controls, E.P.'s learning was not accompanied by conscious knowledge about which answers were correct. He assigned the same confidence ratings to his correct answers as his incorrect answers. Moreover, on the forced-choice test his response times were identical for correct and incorrect responses. Furthermore, unlike controls, he could not respond correctly when the second word in each sentence was replaced by a synonym. Thus, what E.P. learned was rigidly organized, unavailable as conscious knowledge, and in all respects exhibited the characteristics of nondeclarative memory. Thus, factual information, which is ordinarily learned as declarative (conscious) knowledge and with the participation of the medial temporal lobe, can be acquired as nondeclarative memory, albeit very gradually and in a form that is outside of awareness and that is not represented as factual knowledge. We suggest that E.P.'s learning depended on a process akin to perceptual learning and occurred directly within neocortex.
Figures
Fig. 1.
Controls (CON, black bars, n = 4) and E.P. (open bars) studied 48 three-word sentences (e.g., “Shark killed octopus”). Retention tests were given to controls after 2 weeks of study (1 session per week, 2 training trials per session) and to E.P. on 2 consecutive days (T1–T6) after each 4 week study period (2 sessions per week, 2 training trials per session). _A,_Percent correct cued recall of target words in response to the first two words in each sentence. Performance is shown for the pretest (Pre, before study) and after each study period.B, Percent correct forced-choice recognition when the first two words of each sentence were presented together with two possible target words. Performance is shown after each study period. The dashed line shows the score obtained by a group (n = 10) that received no study. Error bars show SEM. Asterisks indicate significant difference versus the no-study group (p < 0.05).
Fig. 2.
Response latencies for correct and incorrect choices in the forced-choice recognition test. For controls (black bars, n = 4), the score was the mean latency for correct and incorrect responses on the 48-item test. Brackets show the SEM of the four scores. For E.P. (open bars), the score was his mean latency across all six forced-choice tests (T1–T6). Error bars show SEM for all his responses.
Fig. 3.
Cued recall performance of E.P. after 12 weeks of study (24 sessions). In the Standard Test, the 48 two-word sentence frames were presented on a computer screen. The score is the average of two tests (T5 and T6 in Fig.1_A_). The Spoken Test was given after the Standard Test at T6. In the Spoken Test, the sentence frames were read aloud by the experimenter.
Fig. 4.
Cued recall performance of target words by controls (black bars, n = 12) and E.P. (open bars) in response to the first two words of each three-word sentence. The score for E.P. is the average of two tests (T5 and T6). Data are for 29 of 48 studied sentences that were given to both E.P. and controls (control data, n = 12; from Hamann and Squire, 1995). In the Standard Test, given to E.P. after 24 sessions of study and to controls after 1 session of study, two-word sentence frames were presented (e.g., “Venom caused ???”), and subjects responded with the target word (fever). In the Synonym Test for E.P., the second word of each sentence frame was replaced by a synonym (e.g., “Venom induced ???”). For the controls, the same synonyms were used for 16 of the sentence frames. For the remaining 13 sentence frames, both words of the sentence frame were replaced by synonyms (e.g., “Venom caused ???” was replaced by “Poison induced ???”). Error bars show SEM.
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