“School of Cognitive Sciences”
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| Paper IPM / Cognitive Sciences / 14329 |
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Locus Coeruleus (LC) neuromodulatory nucleus in the brainstem is known to modulate the activity of individual cells as well as global brain state. Here, we quantified the link between spontaneous LC activity, cortical state and sensory processing in the rat Barrel Cortex (BC). Under urethane anesthesia, we simultaneously recorded unit activity from LC and BC along with prefrontal EEG while presenting brief whisker deflections of various amplitudes. The ratio of low to high frequency components of EEG (referred to as the L/H ratio) identified the cortical state. We found that spontaneous activity of all recorded units in LC exhibited a negative correlation with the L/H ratio. Cross-correlation analysis revealed that changes in LC firing rate preceded changes in state: the cross-correlation function between LC firing profile and L/H ratio showed the strongest correlation at -1.2 s. We further quantified BC neuronal responses to whisker stimulation during the synchronized (high L/H ratio) and desynchronized (low L/H ratio) states. In the desynchronized state, BC neurons showed lower stimulus detection threshold, lower trial-to-trial variability, and shorter response latency. The most prominent change in BC response was observed during the late phase of evoked activity (100-400 ms post stimulus onset): the desynchronized state significantly increased the late response almost for every recorded BC unit. These findings provide evidence for the involvement of the LC norepinephrine neuromodulatory system, in desynchronization of cortical state and a consequent enhancement of sensory coding efficiency.
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