DEFICITS OF VISUAL OBJECT PROCESSING IN TEMPORAL LOBE EPILEPSY: EVIDENCE FROM INTRACRANIAL EVENT-RELATED POTENTIALS
Abstract number :
2.141
Submission category :
Year :
2002
Submission ID :
1374
Source :
www.aesnet.org
Presentation date :
12/7/2002 12:00:00 AM
Published date :
Dec 1, 2002, 06:00 AM
Authors :
Manila Vannucci, Thomas Grunwald, Thomas Dietl, Maria Pia Viggiano, Christoph Helmstaedter, Christian E. Elger. Department of Epileptology, University of Bonn, Bonn, Germany; Department of Psychology, University of Florence, Florence, Italy
RATIONALE: Temporal lobe epilepsies (TLE) are associated with material-specific memory deficits depending on the side of seizure origin. However, while verbal memory deficits in patients with left-sided TLE usually concern long-term storing and delayed recall, visual memory deficits in right-sided TLE involve earlier learning processes instead. Converging evidence from recent neuroimaging and electrophysiological studies now indicates that the medial temporal lobes (MTL) participate in visual object processing. Here, we asked whether the hippocampus proper subserves this function and whether visual memory deficits are associated with deficits of visual object processing in TLE patients.
METHODS: Ninenteen TLE patients (9 left and 10 right) [italic]with [/italic](n=9) or [italic]without [/italic](n=10) visual memory deficits participated in the study.
We recorded intracranial event-related potentials from within the hippocampus proper on the focal and on the non-focal side using a visual object decision task. Patients were asked to discriminate between pictures of real objects and nonsense figures and to name the real objects.
RESULTS: Only in patients [italic]without [/italic] visual memory deficits, neuronal activity of the non-epileptic hippocampus differentiated between both kinds of stimuli: While real objects elicited a pronounced positive component peaking between 500 and 900ms, nonsense figures elicited a marked negative potential in the same time-window. By contrast, in patients [italic]with [/italic] visual memory deficits, similar and less pronounced positive components were elicited by both kinds of stimuli. In all patients neuronal responses were reduced in the epileptic hippocampus whose activity did not differentiate between real objects and nonsense figures.
CONCLUSIONS: Our findings confirm and extend results of earlier studies by demonstrating that the hippocampus proper participates in the semantic processing of visual stimuli. Moreover, our data indicate that this function can be impaired in TLE patients and thus suggest a specific neuropsychological mechanism that may contribute decisively to visual memory deficits in TLE .