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

A sensitive method for the detection of age-related changes Magnetoencephalography (MEG) is a novel, state-of-the-art technique used in clinical neurophysiology, which promises better understanding of brain (dys)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 deep) 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 paradigm (=P300) enables the evaluation of the mechanisms of attentional and intellectual capabilities. Many psychiatric disorders are related to a state of confusion or disturbances of thought. This poster presents a brief report on fundamental and clinical research into cognitive decline during (normal) aging, carried out with our innovative MEG equipment. In healthy subjects asked to discriminate high-pitched 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 that MEG signals yield a more complete image of the complex neuronal interactions involved in this type of cog-nitive 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. Researchers at our Institute are running programs to explore pathophysiological changes in schizo-phrenics, abstinent alcoholics, and Alzheimer patients, in comparison 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 in 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 recordings 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 peak parameters is steeper than described in the literature for an even wider range of ages and pathophysiological situations. …