We studied a group of 31 temporal lobe epilepsy patients (25 left, 6 right)
with unilateral hippocampal sclerosis evident on magnetic resonance imagin
g. Single slice T2 relaxation times were acquired for the left and right hi
ppocampi. Principal components analysis of preoperative memory data resulte
d in two factors that reflect a distinction between arbitrary and semantic
forms of verbal recall. The former component correlated with left hippocamp
al T2 relaxation time, while the latter component did not. This study sugge
sts that variation in left hippocampal integrity is more related to the acq
uisition of arbitrary associates than semantically structured material, and
reinforces the possibility that the left temporal lobe is functionally het
erogeneous with respect to memory.