Hair-Cell Mechanotransduction Persists in TRP Channel Knockout Mice.

Members of the TRP superfamily of ion channels mediate mechanosensation in some organisms, and have been suggested as candidates for the mechanotransduction channel in vertebrate hair cells. Some TRP channels can be ruled out based on lack of an inner ear phenotype in knockout animals or pore properties not similar to the hair-cell channel. Such studies have excluded Trpv4, Trpa1, Trpml3, Trpm1, Trpm3, Trpc1, Trpc3, Trpc5, and Trpc6.

Thalamic synchrony and the adaptive gating of information flow to cortex.

Although it has long been posited that sensory adaptation serves to enhance information flow in sensory pathways, the neural basis remains elusive. Simultaneous single-unit recordings in the thalamus and cortex in anesthetized rats showed that adaptation differentially influenced thalamus and cortex in a manner that fundamentally changed the nature of information conveyed about vibrissa motion. Using an ideal observer of cortical activity, we found that performance in detecting vibrissal deflections degraded with adaptation while performance in discriminating among vibrissal deflections of different velocities was enhanced, a trend not observed in thalamus.

Transient and steady-state dynamics of cortical adaptation.

Adaptation is a ubiquitous property of all sensory pathways of the brain and thus likely critical in the encoding of behaviorally relevant sensory information. Despite evidence identifying specific biophysical mechanisms contributing to sensory adaptation, its functional role in sensory encoding is not well understood, particularly in the natural environment where transient rather than steady-state activity could dominate the neuronal representation. Here, we show that the heterogeneous transient and steady-state adaptation dynamics of single cortical neurons in the rat vibrissa system were well characterized by an underlying state variable.

Nonlinear encoding of tactile patterns in the barrel cortex.

Cells in the rodent barrel cortex respond to vibrissa deflection with a brief excitatory component and a longer suppressive component. The response to a given deflection is thus scaled because of suppression induced by a preceding deflection, causing the neuronal response to be linked to the temporal properties of the peripheral stimulus. A paired-deflection stimulus was used to characterize the postexcitatory suppression and a 3-deflection stimulus was used to investigate the nonlinear response to patterns of whisker deflections in barbiturate-anesthetized Sprague-Dawley rats.

A point process analysis of sensory encoding.

Nowhere is the sparse nature of neuronal coding more evident than in the sensory cortex, where neuronal response becomes increasingly tuned to specific features of the sensory environment. For such situations, where rate modulation schemes do not accurately describe the neuronal response to sensory stimuli, statistical descriptions based on point process events are particularly appropriate. Here, intensity measures derived from experimental data in the rat somatosensory cortex enable the direct analysis of statistical structure within spike trains, as well as inter-relationships between tactile stimuli and neuronal response.