Olson, W. P. | Search bioRxiv

bioRxiv2024

Muscle spindles provide flexible sensory feedback for movement sequences

Sensory feedback is essential for motor performance and must adapt to task demands. Muscle spindle afferents (MSAs) are a major primary source of feedback about movement, and their responses are readily modulated online by gain-controller fusimotor neurons and other mechanisms. They are therefore a powerful site for implementing flexible sensorimotor control. We recorded from MSAs innervating the jaw musculature during performance of a directed lick sequence task. Jaw MSAs encoded complex jaw-tongue kinematics. However, kinematic encoding alone accounted for less than half of MSA spiking variability. MSA coding of kinematics changed based on sequence progression (beginning, middle, or end of the sequence, or reward consumption), suggesting that MSAs are flexibly tuned across the task. Dynamic control of incoming feedback signals from MSAs may be a strategy for adaptable sensorimotor control during performance of complex behaviors.

neuroscience↗

bioRxiv2023

Trigeminal innervation and tactile responses in mouse tongue

The mammalian tongue is richly innervated with somatosensory, gustatory and motor fibers. These form the basis of many ethologically important functions such as eating, speaking and social grooming. Despite its high tactile acuity and sensitivity, the neural basis of tongue mechanosensation remains largely mysterious. Here we explored the organization of mechanosensory afferents in the tongue and found that each lingual papilla is innervated by Piezo2+ trigeminal neurons. Notably, each fungiform papilla contained highly specialized ring-like sensory neuron terminations that asymmetrically circumscribe the taste buds. Myelinated lingual afferents in the mouse lingual papillae did not form corpuscular sensory end organs but rather had only free nerve endings. In vivo single-unit recordings from the trigeminal ganglion revealed lingual low-threshold mechanoreceptors (LTMRs) with conduction velocities in the A{delta} range or above and distinct adaptation properties ranging from intermediately adapting (IA) to rapidly adapting (RA). IA units were sensitive to both static indentation and stroking, while RA units had a preference for tangential forces applied by stroking. Lingual LTMRs were not directly responsive to rapid cooling or chemicals that can induce astringent or numbing sensations. Sparse labeling of lingual afferents in the tongue revealed distinct terminal morphologies and innervation patterns in fungiform and filiform papillae. Together, our results indicate that fungiform papillae are mechanosensory structures, while suggesting a simple model that links the functional and anatomical properties of tactile sensory neurons in the tongue.

neuroscience↗