Cerebral Cortex Advance Access originally published online on March 17, 2006
Cerebral Cortex 2007 17(2):443-456; doi:10.1093/cercor/bhj161
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Changing Frontal Contributions to Memory Before and After Medial Temporal Lobectomy
1 Division of Biology and Biomedical Sciences, 2 Department of Psychology, 3 Department of Anatomy & Neurobiology, 4 Department of Radiology, 5 Department of Howard Hughes Medical Institute, 6 Department of Neurology, 7 Department of Neurological Surgery, Washington University, St Louis, MO, USA
Address correspondence to Luigi Maccotta, MD, PhD, Department of Neurology, University of California, San Francisco, 505 Parnassus Avenue, Box 0114 San Francisco, CA 94143-0114, USA. Email: luigi.maccotta{at}ucsf.edu.
Frontal recruitment was characterized using functional magnetic resonance imaging (fMRI) during memory encoding in temporal lobe epilepsy (TLE) patients before and after unilateral medial temporal lobectomy. Twenty-four TLE patients and 12 healthy controls underwent a preoperative fMRI session consisting of verbal and nonverbal incidental memory-encoding tasks that typically lead to robust, lateralized frontal activity in controls. A similar postoperative fMRI session was performed in a subset of patients. Preoperatively, the verbal task resulted in significant additional recruitment of right frontal cortex in left TLE patients, compared with controls. Right TLE patients instead showed typically lateralized frontal activation. Bilateral frontal recruitment has been observed in older adults and in young adults in situations of difficult task demands. Typical right-lateralized patterns of frontal recruitment were found in both patient groups during the nonverbal task, indicating that the bilateral frontal recruitment pattern was engaged dynamically depending on the task. After surgery, left TLE patients regained more lateralized frontal activity. These results demonstrated differences in frontal recruitment in left and right TLE patients. Such differences emerged in specific task settings and were influenced by surgery, suggesting a dynamic mechanism of frontal recruitment that can be obtained in TLE patients, possibly as a response to presurgical dysfunction.
Key Words: encoding • epilepsy • lateralization • postoperative • prefrontal cortex