VIQ‐PIQ Discrepancies in Partial Epilepsy: On the Relation to Lat‐ eralities of Focal MRI Lesions, P3 Peaks, and Focal Spikes.
Authors: Kanazawa Osamu , Yoshino Mihoko , Sasagawa Mutsuo , Wachi Manabu , Fukuda Masafuini , Kameyama Shigeki 
Published: August 2005

Purpose: A number of previous ncurophysiological studies have indicated that the glutamatergic system is important in the induction of epileptiform activity and the dcvelopment of epileptogenesis. Clutamate transport is the primary mechanism of inactivation of syiiaptically released glutamate. GLAST is classified BS an astrocytic transporter and occurs in high concentrations in the ccrebcllum. The pathophysiologic rolc of GLAST in epilepsy is not known in detail. To investigate the role of thc astroglial glutamatc transporter GLAST in epileptogenesis, we compared amygdalu‐kindling and pentylenctetrazolc (PTZ) induced seizures in GLAST‐deficient mice (GLAST(‐/‐)) wild‐type mice (GLAST(+/+)), and maternal C57Black6/J mice (C57).

Purpose: Subtest IQ such as verbal IQ (VIQ) and performance IQ (PIQ) in WAIS or WISC are thought to represent neuropsychological functions of the left and right hemispheres, respectively. The P300 (P3) event‐related potential reflects cognitive processes. We do not ye1 know the brain site of P3 origin or how epileptogenic foci (EF) influ‐ ence P3 potentials. To examine neuropsychological influence by partial epilepsy (PE), we studied VIQ‐PIQ discrepancies in PE in relation to lateralities of focal MRI lesions, P3 peaks, and EF.

Methods: Thirteen patients showed VIQ‐PIQ discrepancies significant at the p7lt;O.O5 level, represented by a>l2‐point spread for the WAIS in adults, and a 15‐point spread in the WISC in children. We evoked P3 potentials in the individuals with discrepant IQ differences by asking them to keep a mental count of rare tones, including introduction of oddbail tones. EEGs were recorded by the international 10–20 system and P3 peaks were shown in a topographical view by offline analysis. Patients were divided into normal and abnormal groups according to MRI findings, and were examined for the laterali‐ ties of the dominant side in subtest IQ (conventionally, we regarded higher VIQ as left hemisphere dominant and higher PIQ as right hemisphere dominant), P3 peaks, and EF. We did not correlate results with lert or right handedness.

Results: Five patients (38.5%) were in the normal group and 8 patients (61.5%) were in the abnormal group. Concordance of the lateralities in P3 peaks and dominant side in subtest IQ was shown in 1 patient (20%) in the normal group and 5 patients (62.5%) in the abnormal group. In the normal group, all patients showed contralateral P3 peak shift to EF, and all except I patient showed contralateral P3 peak shift to the dominant side in subtest IQ. The other 3 patients in the abnormal group showed unilateral focal cortical dysplasias (FCD), ipsilateral P3 shift, and contralateral dominant side in subtest IQ to the focal MRI lesions.

Conclusion: In our partial epilepsy series with VIQ‐PIQ discrepancies, concordance of the lateralities in P3 peaks and dominant side in subtest IQ was shown in < half of the patients. Epileptogenic foci seem to have 3 different grades of influence on P3 peak shift and dominant side in subtest IQ according to the severities of accompanying focal MRI lesions: 1. Without MRI lesions, EF can make P3 peak shift contralaterally, but the dominant side in the subtest IQ shift ipsilaterally; 2. With less severe focal MRI lesions such as hippocampal atrophy etc., EF can make not only P3 peaks but also the dominant side in the subtest IQ shift contralaterally; 3. With severe focal MRI lesions such as FCD, EF can make the dominant side in the subtest IQ shift contralaterally, but the P3 peak may shift ipsilaterally. Epileptogenic foci without MRI lesions seem to control ipsilateral P3 potentials. MRI lesions render a hemisphere unlikely to become dominant, but epileptogenic foci can coexist with apparently normal neuropsychological function.