Coordenação de ritmos sensório-motores durante comportamento exploratório em ratos

Abstract

When actively exploring the environment, rats exhibit several rhythmic behaviors with frequencies in the theta range (5-10 Hz). These include sniffing (active fast respiration), whisking (movement of the facial vibrissae), and ultrasonic vocalizations. Synchronizations between each pair of these behaviors have been observed in recent studies: vibrissae protraction-retraction is linked to the inhalation-exhalation phase of breathing; constriction of the vocal folds for vocalization, in turn, is locked to the exhalation phase of sniffing; accordingly, vocalizations were observed to synchronize with the retraction phase of whisking. These and other observations point to an interaction of rhythm and pattern generators in the brainstem controlling the coordination of respiratory, oral and facial movements. To better understand the hierarchies among these circuits we simultaneously recorded sniffing, whisking and vocalizations from rats during free social exploration. For this purpose, eight electrodes were inserted surgically to acquire bilateral EMG signals from muscles controlling the protraction and retraction of the whiskers and a cannula was implanted through the nasal bone to record the respiratory cycle. After one week of recovery and habituation, two rats (one implanted and one naive) were placed across a gap where they could explore each other. These interactions were filmed with a high speed camera (250 Hz) to capture whisker movements and ultrasonic vocalizations were recorded from an overhanging microphone. We made frequency and phase analysis to validate the recorded signals and characterize the interplay between these sensorimotor rhythms. Results confirmed that both sniffing and whisking occur in bouts at theta frequencies during social exploration. Furthermore, we observed the expected anti-phase relationship between the EMGs from muscles controlling whisker protraction and retraction as well as their tight synchrony with the sniffing cycle. Interestingly, our data suggests that this synchrony is immediately lost during the emission of ultrasonic vocalizations. Instead, we observed a novel whisking behavior, consisting of active vibrissae protraction and retraction independent of the respiratory cycle.