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| Paper IPM / Cognitive / 14331 |
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Introduction: In order to adapt to various environmental and behavioral demands, the brain can switch between multiple modes of processing. Through changes of cortical state, sensory pathways alter information transmission by modulating the spontaneous pattern of neuronal activity and the profile of sensory responses. Locus Coeruleus (LC) as a major neuromodulatory system in the brainstem has widespread projections throughout the brain and is known to modulate the activity of cells and network states. Methods: Here, we quantified the link between the LC spontaneous activity, cortical state and sensory processing in the rat barrel cortex (BC). We simultaneously recorded unit activity from LC and BC along with prefrontal EEG while presenting brief whisker deflections of various amplitudes under urethane anesthesia. The ratio of low to high frequency components of EEG (referred to as the L/H ratio) was employed to identify the cortical state. Results: We found that the 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 the cortical state: the correlation of the LC firing profile with the L/H ratio
was maximal at a lag of -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, higher
response fidelity, and shorter response latency. The most prominent change was observed in the late phase of BC evoked activity (100-400 ms post stimulus onset): almost every recorded BC unit exhibited a greater late response during the desynchronized state compared to the synchronized state. Highly similar response profiles were obtained from categorization of trials based on LC activity (high and low LC discharge) or cortical state (low and high L/H ratio). Conclusion: These findings provide evidence for the involvement of the LC norepinephrine neuromodulatory system, LC-NE, in the desynchronization of cortical state and a consequent
enhancement of sensory coding efficiency.
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