Medial temporal lobe volume predicts rate of learning in Rey-AVLT

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.