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Abstract:
Functional imaging studies implicate dorsolateral frontal
regions in encoding and retrieval processes. However, lesions in
these regions are not associated with significant memory
disruption. Using cortical stimulation mapping in patients with
epilepsy, we assessed whether temporary lesions (from electrical
stimulation) of frontal cortex are sufficient to disrupt memory.
Stimulation was performed through grid electrodes placed in 8
patients (all left dominant for language, 4 left- and 4 right-sided
grids). A delayed recall task was performed with each trial
consisting of four slides (4s each). Slide 1 was a picture naming
task. Slides 2 and 3 were distracter reading tasks. Slide 4 cued
the patient to recall the picture in Slide 1. At each cortical
site, stimulation was applied either during encoding (naming of the
picture), during the distracter task, or during recall. For each
trial, stimulation was applied only once. A cortical map was
obtained in six patients (3/4 on each side). All six patients
showed dorsolateral cortex sites where either encoding or retrieval
was disrupted. In no sites were both processes disrupted. The
expanse of sites involved was larger for left-sided grids, but
right-sided sites were found in homologous regions that matched
regions of activation in imaging studies. These findings confirm a
critical role for dorsolateral frontal cortex in memory encoding
and retrieval, possibly related to working memory processes.
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