engleski

Neuromagnetic study of the auditory gating phenomenon

The amplitude variability of the M50 component of the auditory neuromagnetic responses is commonly used to explore the brain’s ability to modulate its sensitivity to incoming auditory stimuli, a process conceptualized as the gating mechanism. Despite many studies of the gating network topology, it remains an open question. The goal of this study was to identify the spatial and temporal characteristics of the cortical sources underlying the M50 complex evoked by the tones of a passive oddball paradigm (1 kHz, p=0.8 ; 1.2 kHz, p=0.2). Twenty elderly subjects (10 healthy and 10 patients diagnosed with Alzheimer's type dementia in mild and advanced stages) were examined using magnetoencephalographic recordings (CTF 275- channel whole-head system, VSM MedTech, Ltd.) in a magnetically shielded room at the MIND Research Network in Albuquerque, New Mexico and the multi- dipole Calibrated Start Spatio-Temporal (CSST) source localization method. We identified three cortical regions underlying the M50 network: prefrontal cortex (PF) in addition to bilateral activations of superior temporal gyri (STG). We characterized the cortical dynamics of the PF source within the 30-100 ms post-stimulus interval and found that it is comprised of two subcomponents peaking successively at 46-50 ms (Mb1c) and 80-88 ms (Mb2c) post-stimulus. The PF source was localized for 10/10 healthy subjects, whereas 9/10 demented patients were lacking the PF source for both tone conditions. The selective activation of the PF source within the M50 network according to subject diagnostic categories enabled a differential analysis of the functional relation between individual sources within the network. We found significantly enhanced activity of the STG sources in both tone conditions for all subjects who lacked a PF source. Reported results provide novel insights into the topology and neurodynamics of the M50 auditory network and suggest an inhibitory role of the PF source that suppressed activity of the STG sources in the auditory gating phenomenon.

agnetoencephalography (MEG); evoked neuromagnetic fields; biomagnetic inverse problem; spatio-temporal localization; neurodynamics; sensory processing; oddball paradigm; auditory M50 component; gating in; gating out; prefrontal cortex (PF); primary auditory cortex (STG)

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