Abstract
Whisker movements are used by rodents to touch objects in order to extract spatial and textural tactile information about their immediate surroundings. To understand the mechanisms of such active sensorimotor processing it is important to investigate whisker motor control. The activity of neurons in the neocortex affects whisker movements, but many aspects of the organization of cortical whisker motor control remain unknown. Here, we filmed whisker movements evoked by sequential optogenetic stimulation of different locations across the left dorsal sensorimotor cortex of awake head-restrained mice. Whisker movements were evoked by optogenetic stimulation of many regions in the dorsal sensorimotor cortex. Optogenetic stimulation of whisker sensory barrel cortex evoked retraction of the contralateral whisker after a short latency, and a delayed rhythmic protraction of the ipsilateral whisker. Optogenetic stimulation of frontal cortex evoked rhythmic bilateral whisker protraction with a longer latency compared to stimulation of sensory cortex. Compared to frontal cortex stimulation, larger amplitude bilateral rhythmic whisking in a less protracted position was evoked at a similar latency by stimulating a cortical region posterior to Bregma and close to the midline. These data suggest that whisker motor control might be broadly distributed across the dorsal mouse sensorimotor cortex. Future experiments must investigate the complex neuronal circuits connecting specific cell-types in various cortical regions with the whisker motor neurons located in the facial nucleus.
Highlights
Rodents use their array of mystacial whiskers to obtain tactile information about their immediate facial surroundings (Brecht, 2007; Petersen, 2007; Diamond et al, 2008; Bosman et al, 2011; Feldmeyer et al, 2013)
Our results indicate that whisker movements can be evoked by stimulating many cortical regions, with short latency retraction of contralateral whiskers being evoked from wS1, and rhythmic bilateral whisker protraction being evoked by stimulation of other cortical areas including a frontal and a more posterior midline cortical region
The amplitude of whisker movements occurring within the frequency range of 5–15 Hz (Fig. 6) for both right and left C2 whiskers was computed for each trial as the integral between 5 Hz and 15 Hz of the fast Fourier transform (FFT) of whisker angle during the last 400 ms of the optogenetic stimulation
Summary
Rodents use their array of mystacial whiskers to obtain tactile information about their immediate facial surroundings (Brecht, 2007; Petersen, 2007; Diamond et al, 2008; Bosman et al, 2011; Feldmeyer et al, 2013). Electrical stimulation of different cortical regions evoked different movements, with the most important region, the primary motor cortex (M1), being located in the frontal cortex, anterior to the central sulcus. Experiments in rodents suggested that movements could be evoked by stimulating many different regions of the neocortex (Hall and Lindholm, 1974; Donoghue and Wise, 1982; Gioanni and Lamarche, 1985; Neafsey et al, 1986). In awake head-restrained mice, stimulation of the primary somatosensory whisker barrel cortex (wS1) has been proposed to evoke retraction of the contralateral whisker, whereas the direct effect of stimulation of a frontal region wM1, which is strongly innervated by wS1, is proposed to drive rhythmic whisker protraction (Matyas et al, 2010; Petersen, 2014; Sreenivasan et al, 2015, 2016). Our results indicate that whisker movements can be evoked by stimulating many cortical regions, with short latency retraction of contralateral whiskers being evoked from wS1, and rhythmic bilateral whisker protraction being evoked by stimulation of other cortical areas including a frontal and a more posterior midline cortical region
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