The relationship between magnetic and electrophysiological responses to complex tactile stimuli

<p>Abstract</p> <p>Background</p> <p>Magnetoencephalography (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.</p> <p>Results</p> <p>Signal 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.</p> <p>Conclusion</p> <p>The 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.</p

The relationship between magnetic and electrophysiological responses to complex tactile stimuli.

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

DNA and cultures of remembrance: anthropological genetics, biohistories and biosocialities

The article engages current human population genetic research or anthropological genetics with an emphasis on its popular forms. A general discussion of the production of biohistories on the basis of DNA analyses is elaborated by focusing on what I call the Genographic network: the Genographic Project and the associated genetic ancestry companies as well as book and film productions. In order to gain an understanding of the specificity of what is also referred to as genetic history, the development of notions such as a genetic heritage, the gene as historical document, and the DNA as archive of history are briefly treated, before approaching the recent commercializations and medializations of group-specific and personalized genetic history and identity. It is here that the challenge of joining history and DNA becomes most evident: on the one hand, the genetic knowledge is presented as particularly authentic and accurate on the basis of its epistemic objects and quantitative and technological approaches. On the other hand, in order for biohistorical identities and socialities to form, the knowledge needs to be rendered in a narrative, esthetically appealing way. This also points to differences vis-à-vis medical genomics in that neither anthropological genetics, nor the biosocialities it facilitates, are oriented towards hope for future health solutions. In offering supposedly purely anthropological knowledge about who we are and where we come from, anthropological genetics is part of backward-looking socialities. It is part of cultures of remembrance