Abstract
The medial temporal lobe (MTL) has been assigned a central role in human episodic memory and learning. Evidence for this comes from PET and fMRI studies as well as lesion studies. This study aimed at comparing the effect of atrophy at repeated trials of a supraspan test of memory. Included in the study were patients with Alzheimer’s Disease, Mild Cognitive Impairment, and Subjective Memory Disorders as well as Controls (n = 116). The supraspan test used was the Rey Auditory Verbal Learning test (RAVLT). Comparisons between extreme groups with high (Stanine 6 - 9) and low (Stanine 1 - 4) intracranial proportions (IP) of MTL were made at the five trials of RAVLT. There was a significantly higher rate of learning among subjects with high MTL IP compared to those with low MTL IP in both hemispheres. There was no difference in the rate of list learning performance due to education or age and interestingly: the list learning rates among subjects with high/low Lateral Temporal Lobe IPs were almost similar. The hemispheric differences regarding learning rate were small and insignificant. Results are discussed in terms of hippocampal involvement in associative processes necessary in supraspan list learning.
Highlights
The medial temporal lobe (MTL) including the hippocampus has been tied to one or all of the main episodic memory functions: encoding, storage and/or retrieval
There was no significant effect of Right Lateral Temporal Lobe (RTL) proportion on Rey Auditory Verbal Learning test (RAVLT) scores (F < 1) and there was no significant interaction between trials and RTL volume, Rao R(4, 81) = 0.26, p = 0.90, When age and education were entered as covariates, there were no significant within cells regressions, Rao R Form 3 (10, 158) = 0.97, p = 0.47, see Figure 1
There was a tendency of an Lateral Temporal lobe (LTL) effect on RAVLT scores, F (1, 80) = 3.75, p = 0.06, but there was no interaction between trials and LTL volume, Rao R (4, 67) = 0.25, p = 0.91, see Figure 2
Summary
The medial temporal lobe (MTL) including the hippocampus has been tied to one or all of the main episodic memory functions: encoding, storage and/or retrieval Different views regarding this function of MTL have been proposed. The encoding and retrieval hypothesis, holds that the hippocampal system binds different components of an event by linking simultaneous activation in distributed brain regions [1,2,3,4]. According to this theory hippocampus should be activated both during encoding and retrieval. Both of these theories implicate hippocampal involvement in learning new associations
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