Magnetoencephalography of cognitive responses A sensitive method for the detection of age-related changes

Abstract

Magnetoencephalography (MEG) is a novel, state-of-the-art technique used in clinical neurophysiology, which promises better understanding of brain (days) function. The “whole-head” MEG sensor-array enables a noninvasive visualization of the intracellular currents involved in transmission and processing of information in the working brain, on a millisecond timescale, taking into account all (superficial and deeps) parts of the CNS simultaneously. 3D reconstruction algorithms are used to attribute sources to anatomically defined structures and cortical subdivisions. MEG recording during the performance of a simple decision-making task using a continuous Go-NoGo puradigm (= P300) enables the evaluation of the mechanism of attentional and intellectual capabilities. Many psychiatric disorders are related to a state of confusion or disturbances of thought. This poster presentsa brief report on fundamental and clinical research into cognitive decline during (normal) aging, carried out with our innovative MEG equipement. In healthy subjects asked to discriminate high-piched target tones among standard tones during an oddball detection task, when attention is correctly directed, a particular transient electrical potential is observed, called P300,1 with maximal amplitudes around the vertex. The underlying generators are thought to be located in the medial temporal lobe regions. We recently demonstrated tha MEG signals yeld a more complete image of the complex neuronal intercactions involved in this type of cognitive response, showing a large positive pole over the left precentral and frontal brain regions (Figure 1) and a mirror image pattern in the right hemisphere (not shown).2 We are currently in the process of localizing the sources in a realistic head model. Figure 1. Top: 3D mapping of positive pole of MEG response to target tones. Bottom: averaged tracings in Broca's area for 2 age groups (young [ 300 ms (horizontal scale 100 ms/division). ... Research at our Institute are running programs to explore pathophysiological changes in schizophrenics, abstinent alcoholics, and Alzheimer patients, in comparaison with normal aging in control subjects. This is achieved by plotting amplitude and latency parameters for individual subjects as a function of age (Figure 2). Significant decline is found subjects at the far ends of our age-range. Regression analysis shows a loss of signal of about 15% with a slowing of 10 to up to 20 ms with every decade of life. Preliminary findings indicate that MEG recording are able to evidence age-related changes, as do electrical responses, and that these are already clearly visible before the age of 50 years. The slope of change in signal speak parameters is steeper than described in the literature for a neven wider range of ages and pathopysiological situations.9 Figure 2. A. Scattergram of amplitude (ampl) for target specific MEG response in Broca's area B. Mean amplitude of electrical response (P300, Cz electrode) in young (Δ) and aged ( ) healthy subjects; C. Scattergram of MEG response latency; D. mean latency ...