Much of what we know about visual processing in the brain is based on neural data collected in anesthetized animals assuming that the essential aspects of the computations are preserved under such conditions. However, recent findings support an alternative view on visual perception that puts a strong emphasis on the role of ongoing activity which is all but eliminated in anesthetized preparations. According to this view, spontaneous activity represents momentary biases, contextual information and internal states of the brain that are essential for interpreting the incoming sensory information. Thus it is critical to understand what aspects of spontaneous activity carry relevant information for perception. To study this question, we collected and analyzed multi-electrode recordings in the primary visual cortex of adult rats under different levels of anesthesia. Anesthesia was induced by isoflourane ranging from 1.0 to 3.0% in increments of 0.5%. Isolated unit and local field potential (LFP) activity was collected from sixteen electrodes. Coherence analysis on LFPs revealed a clear increase from low to high levels of isoflurane anesthesia. Specifically, the mean coherence between electrodes over the LFP frequency range decreased with each increase in isoflurane concentration, from 1.0% to 3.0%. Variation about the mean also increased with higher levels of anesthesia. In addition, peaks in correlation were broader under light levels of anesthesia than under deep levels. Therefore, isoflurane anesthesia seems not only to reduce overall levels of cortical activity, but also to decrease the amount of correlation and coherence in ongoing activity. These results suggest that ongoing activity in the primary visual cortex of the rat has a structure that is appropriate for conveying relevant information for visual processing. In contrast to the presently dominant feed-forward view on perceptual processing, using this information requires a rapid dynamic integration of bottom-up an top-down signals in the primary visual cortex.

Leave a Reply

Your email address will not be published. Required fields are marked *