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要旨:
Neurons in auditory cortex are selective for the frequency content of acoustical stimuli.
Classically, this response selectivity is studied at the single neuron level. However, current
research often employs functional imaging techniques to investigate the organization of
auditory cortex. The signals underlying the imaging data arise from neural mass action and
reflect the properties of populations of neurons. For example, the signal used for functional
magnetic resonance imaging (fMRI-BOLD) was shown to correlate with the oscillatory
activity quantified by local field potentials (LFP). This raises the questions of how the
frequency selectivity in neuronal population signals compares to the tuning of spiking
responses. To address this, we quantified tuning properties of auditory evoked potentials
(AEP), different frequency bands of the LFP, analog multi-unit (AMUA) and spike-sorted
single- and multi-unit activity in auditory cortex.
The AMUA showed a close correspondence in frequency tuning to the spike-sorted
activity. In contrast, for the LFP we found a clear dissociation of high and low frequency
bands: there was a gradual increase of tuning-curve similarity, tuning specificity and
information about the stimulus with increasing LFP frequency. While properties of the high
frequency LFP matched those of spiking activity, the lower frequency bands differed
considerably, as did the AEP. These results demonstrate that electrophysiological population
responses exhibit varying degrees of frequency tuning and suggest that those functional
imaging methods that are related to high frequency oscillatory activity should well reflect the
neuronal processing of sound frequency.
