Heterogeneity in the coding in rat barrel cortex of the velocity of protraction of the macrovibrissae

Abstract

Rats whisk to explore their environment and obtain information on object features, and the responses of somatosensory cortical neurones must precisely encode aspects of whisker movements. Using trapezoidal stimuli to deflect whiskers, with a wide range of velocities and amplitudes of whisker protraction, we recorded responses from a relatively homogeneous population of isolated cells and neuronal multiunits within the postero-medial barrel sub-field of somatosensory cortex, and analysed responses in an early post-stimulus-onset window. For 92% of neurones the function relating response strength to velocity was a saturating sigmoid but there were differences between neurones in the slopes and ranges over which responses changed. Responses of other neurones were non-monotonic, with response strength decaying at very high whisker deflection velocities. Generally, barrel cortex neurones were responsive to a much wider range of whisker protraction velocities than hitherto reported, especially to much slower velocities than generally assumed to be the main range of sensitivity. This carries implications for coding of whisker deflection velocity, a parameter that appears to be a significant information-bearing element of natural whisking. The effect of amplitude of deflection upon neural responses was evident in only approximately 24% of units and only when the dominant velocity effect had saturated.

The Acute Phase of Mild Traumatic Brain Injury Is Characterized by a Distance-Dependent Neuronal Hypoactivity

“…At 24 h post-surgery, electrophysiological recordings from posteromedial barrel subfield (PMBSF; barrel cortex) were obtained using methods previously established in our group, 17,31,32 at both ipsilateral and contralateral locations relative to the site of injury. Animals were anesthetized using 5% halothane and tracheotomized to maintain anesthesia at 0.5-3.0% halothane through continuous ventilation.…”

“…A craniotomy over the barrel cortex (either ipsilateral or contralateral to injury; approximately 4 mm diameter, centered approximately A/P -2 mm to bregma; M/L 6 mm) was made via drilling, and the exposed barrel cortex (with dura intact) was penetrated with a tungsten microelectrode (2-4 MOhm; FHC) using a fast-stepping microdrive (Kopf Model 2660) mounted on a complex of translators and goniometers. 31,32 Advancement of the electrode was monitored via high-power microscopy, by monitoring electrode depth on the calibrated microdrive, and by monitoring the amplified and filtered electrode output through speakers and on an oscilloscope.…”

“…31,32 After unequivocal determination of the PW, the electrode was retracted to the surface, rezeroed again under high-powered microscopy, and then advanced systematically in 10-lm steps to record from the various cortical laminae, while monitoring depth on the microdrive.…”

Progesterone sharpens temporal response profiles of sensory cortical neurons in animals exposed to traumatic brain injury.

“…A craniectomy exposed the right barrel cortex (*2 mm caudal to bregma, 6 mm lateral to the midline) with dura left intact. Under high-power microscopy, a tungsten microelectrode (2 to 4 MO; FHC, Bowdoin, ME), held in a calibrated microdrive (Model 2660, David Kopf Instruments, Tujunga, CA, USA) mounted on a custom rig of translators and goniometers, 36,37 was positioned to make light contact with the pia. The microdrive was zeroed with the microelectrode tip placed on the cortical surface, and the microdrive was used to rapidly advance the electrode to between 600 and 800 mm from the surface which has been explained in more detail elsewhere.…”

“…The microdrive was zeroed with the microelectrode tip placed on the cortical surface, and the microdrive was used to rapidly advance the electrode to between 600 and 800 mm from the surface which has been explained in more detail elsewhere. 37 The electrode was allowed to settle in place here and then the principal whisker (PW; the whisker providing main excitatory input) was determined from manual whisker deflections. If a single PW was identifiable, further recordings were obtained with stimuli applied under automated control; if unidentifiable, the microelectrode was removed from the cortex and repositioned elsewhere to repeat the process until a single PW could be identified in a recording site.…”