Abstract
BackgroundMagnetoencephalography (MEG) has become an increasingly popular technique for non-invasively characterizing neuromagnetic field changes in the brain at a high temporal resolution. To examine the reliability of the MEG signal, we compared magnetic and electrophysiological responses to complex natural stimuli from the same animals. We examined changes in neuromagnetic fields, local field potentials (LFP) and multi-unit activity (MUA) in macaque monkey primary somatosensory cortex that were induced by varying the rate of mechanical stimulation. Stimuli were applied to the fingertips with three inter-stimulus intervals (ISIs): 0.33s, 1s and 2s.ResultsSignal intensity was inversely related to the rate of stimulation, but to different degrees for each measurement method. The decrease in response at higher stimulation rates was significantly greater for MUA than LFP and MEG data, while no significant difference was observed between LFP and MEG recordings. Furthermore, response latency was the shortest for MUA and the longest for MEG data.ConclusionThe MEG signal is an accurate representation of electrophysiological responses to complex natural stimuli. Further, the intensity and latency of the MEG signal were better correlated with the LFP than MUA data suggesting that the MEG signal reflects primarily synaptic currents rather than spiking activity. These differences in latency could be attributed to differences in the extent of spatial summation and/or differential laminar sensitivity.
Highlights
Magnetoencephalography (MEG) has become an increasingly popular technique for non-invasively characterizing neuromagnetic field changes in the brain at a high temporal resolution
Data gathered from studies using positron emission tomography (PET) and functional magnetic resonance imaging have enhanced our knowledge of normal processing in the cerebral cortex, as well as deficits related to disease states
We examined the relationship between the MEG signal, local field potentials and multiunit activity in the same animal using calibrated mechanical stimuli delivered at varying rates of stimulation
Summary
Magnetoencephalography (MEG) has become an increasingly popular technique for non-invasively characterizing neuromagnetic field changes in the brain at a high temporal resolution. Data gathered from studies using positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) have enhanced our knowledge of normal processing in the cerebral cortex, as well as deficits related to disease states. While these techniques are widely used to study aspects of brain organization and function, there are limitations regarding their use and the types of information that can be obtained. A less widely used technique, magnetoencephalography (MEG), is a non-invasive method for detecting and characterizing changes in neuromagnetic fields in the brain. Since its introduction by Cohen in 1972 [3], MEG has proven useful for clinical applications and basic science research [1,2]
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