Abstract
Objectives: Medial temporal lobe epilepsy (mTLE) is characterized by decreased hippocampal volume, which results in motor memory consolidation impairments. However, the extent to which motor memory acquisition are affected in humans with mTLE remains poorly understood. We therefore examined the extent to which learning of a motor tapping sequence task is affected by mTLE.Methods: MRI volumetric analysis was performed using a T1-weighted three-dimensional gradient echo sequence in 15 patients with right mTLE and 15 control subjects. Subjects trained on a motor sequence tapping task with the left hand in right mTLE and non-dominant hand in neurologically-intact controls.Results: The number of correct sequences performed by the mTLE patient group increased after training, albeit to a lesser extent than the control group. Although hippocampal subfield volume was reduced in mTLE relative to controls, no differences were observed in the volumes of other brain areas including thalamus, caudate, putamen and amygdala. Correlations between hippocampal subfield volumes and the change in pre- to post-training performance indicated that the volume of hippocampal subfield CA2–3 was associated with motor sequence learning in patients with mTLE.Significance: These results provide evidence that individuals with mTLE exhibit learning on a motor sequence task. Learning is linked to the volume of hippocampal subfield CA2–3, supporting a role of the hippocampus in motor memory acquisition.Highlights -Humans with mTLE exhibit learning on a motor tapping sequence task but not to the same extent as neurologically-intact controls.-Hippocampal subfield volumes are significantly reduced after mTLE. Surrounding brain area volumes do not show abnormalities.-Hippocampal subfield CA2–3 volume is associated with motor sequence learning in humans with mTLE.
Highlights
MATERIALS AND METHODSThe hippocampus is involved in procedural memory, a type of memory necessary for motor sequence learning (Albouy et al, 2013)
Post hoc tests indicated that volume size of all hippocampal subfields was less in the Medial temporal lobe epilepsy (mTLE) group compared to the control group: fimbria (F(1,15) = 11.7, P < 0.001), CA1 (F(1,15) = 12.4, P < 0.001), CA2-CA3 (F(1,15) = 15.3, P < 0.001), CA4-dentate gyrus (DG) (F(1,15) = 8.1, P < 0.001), subiculum (F(1,15) = 7.8, P < 0.001), and presubiculum (F(1,15) = 10.5, P < 0.001)
Post hoc tests indicated that volume size of all hippocampal subfields but the hippocampal fissure in the right hemisphere was less in the mTLE group compared to the control group
Summary
MATERIALS AND METHODSThe hippocampus is involved in procedural memory, a type of memory necessary for motor sequence learning (Albouy et al, 2013). During a serial reaction time task, amnesic patients have been shown to outperform controls by repeating the sequence of key presses to the location of the stimulus through increasingly rapid performance. These same patients exhibit an impaired ability to recognize the sequence (Reber and Squire, 1998). Decreased hippocampal volume ipsilateral to the epileptogenic temporal lobe has been reported in this patient population (Marsh et al, 1997). At present, it is not known whether motor sequence learning is preserved in humans with mTLE
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