Posters & images in neuroscience Magnetoencephalography of cognitive responses 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 process- ing 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 continu- ous   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 tempo- ral lobe regions.We recently demonstrat- ed that MEG signals yield a more com- plete 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 real- istic 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 sub- jects. 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 elec- trical 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.9 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 [<25 y] ––; mid-age [34-47 y],      ). Note the sustained positive wave >300 ms (horizontal scale 100 ms/division). 1 8 2 Intermezzo 1 In the aging brain, a general attenuation of the P300 response with a slowing of the time to reach the peak in drug- free volunteers (Figures 1 and 2C, D) is reported.3 In young healthy volunteers, this response, characterized by its peak amplitude and peak latency, is known to be at least partly under cholinergic control4,5 and can be enhanced by psychotropic drugs.6 In the elderly, nootropic drugs are able to achieve a significant, restoration of P300.7,8 The proven relationship between psychopharmacology, conscious attention, evoked (cognitive) responses and brain anatomy is a cornerstone concept in biological psychiatry research.
Vol 1 n° 3 - Nosology and Nosography
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