Power spectral density changes and language lateralization during covert object naming tasks measured with high-density EEG recordings

C Ramon,Maciej Gratkowski,K.J Eriksen,M Holmes,Jens Haueisen,Walter J Freeman

doi:10.1016/j.yebeh.2008.08.018

Abstract

Our objective was to study changes in EEG time-domain power spectral density (PSDt) and localization of language areas during covert object naming tasks in human subjects with epilepsy. EEG data for subjects with epilepsy were acquired during the covert object naming tasks using a net of 256 electrodes. The trials required each subject to provide the names of common objects presented every 4 seconds on slides. Each trial comprised the 1.0 second before and 3.0 seconds after initial object presentation. PSDt values at baseline and during tasks were calculated in the theta, alpha, beta, low gamma, and high gamma bands. The spatial contour plots reveal that PSDt values during object naming were 10-20% higher than the baseline values for different bands. Language was lateralized to left frontal or temporal areas. In all cases, the Wada test disclosed language lateralization to the left hemisphere as well.

Highlights

Cerebral lateralization of essential language activity is an important component of the evaluation of patients with medically refractory epilepsy who are candidates for surgical therapy
These plots reveal that power spectral density (PSDt) values during the object naming tasks were approximately 5–20% higher than baseline values in the anterior left quadrant of the plots
There is an increase in PSDt values in the lower right and left edges of the plots in the h band

Summary

Introduction

Cerebral lateralization of essential language activity is an important component of the evaluation of patients with medically refractory epilepsy who are candidates for surgical therapy. For more than a half-century the intracarotid sodium amytal procedure, known as Wada test, has been the standard by which this determination has been made [1]. The Wada test is associated with some risk and discomfort. In recent years, a burgeoning interest has developed in replacing the Wada test with noninvasive measures. Some of these newer techniques, like the Wada test, are based on ‘‘deactivation” of the language cortex, such as repetitive transcranial magnetic stimulation [2], whereas other methods are based on structural imaging analyses [3]. The most promising novel noninvasive methods include direct measures of physiological language activation. The other alternative activation techniques are based on hemodynamic responses to language activation, such as functional

Objectives

Methods

Results

Conclusion