Abstract: In vivo studies of neurophysiology using the whole cell patch-clamp technique enable exquisite access to both intracellular dynamics and cytosol of cells in the living brain but are underrepresented in deep subcortical nuclei because of fouling of the sensitive electrode tip. We have developed an autonomous method to navigate electrodes around obstacles such as blood vessels after identifying them as a source of contamination during regional pipette localization (RPL) in vivo. In mice, robotic navigation prevented fouling of the electrode tip, increasing RPL success probability 3 mm below the pial surface to 82% (n = 72/88) over traditional, linear localization (25%, n = 24/95), and resulted in high-quality thalamic whole cell recordings with average access resistance (32.0 MΩ) and resting membrane potential (−62.9 mV) similar to cortical recordings in isoflurane-anesthetized mice. Whole cell yield improved from 1% (n = 1/95) to 10% (n = 9/88) when robotic navigation was used during RPL. This method opens the door to whole cell studies in deep subcortical nuclei, including multimodal cell typing and studies of long-range circuits.
New & noteworthy: This work represents an automated method for accessing subcortical neural tissue for intracellular electrophysiology in vivo. We have implemented a novel algorithm to detect obstructions during regional pipette localization and move around them while minimizing lateral displacement within brain tissue. This approach leverages computer control of pressure, manipulator position, and impedance measurements to create a closed-loop platform for pipette navigation in vivo. This technique enables whole cell patching studies to be performed throughout the living brain.
W. A. Stoy, I. Kolb, G. L. Holst, Y. Liew, A. Pala, B. Yang, E. S. Boyden, G. B. Stanley, C. R. Forest
Journal of Neurophysiology Published 1 August 2017 Vol. 118 no. 2, 1141-1150 DOI: 10.1152/jn.00117.2017 PDF
A pervasive underlying assumption about sensory processing is that neural activity represents the world in a graded manner: the stronger the input, the stronger the response; the weaker the input, the weaker the response. In work from Dr. Clare Gollnick and colleagues, this assumption was directly considered and investigated through voltage sensitive dye imaging of activity across somatosensory cortex in the representation of tactile inputs. Experimental evidence and theoretical analyses suggest that an alternative strategy may be at work, in which populations of neurons encode information in a more binary, probabilistic manner, and that the information is represented in a more distributed manner across the larger population. Read the full article for more… Gollnick2016b
The ability to perceive the direction of whole-body motion during standing may be critical to maintaining balance and preventing a fall. Our first goal was to quantify kinesthetic perception of whole-body motion by estimating directional acuity thresholds of support-surface perturbations during standing. The directional acuity threshold to lateral deviations in backward support-surface motion in healthy, young adults was quantified as 9.5 ± 2.4° using the psychometric method (n = 25 subjects). However, inherent limitations in the psychometric method, such as a large number of required trials and the predetermined stimulus set, may preclude wider use of this method in clinical populations. Our second goal was to validate an adaptive algorithm known as parameter estimation by sequential testing (PEST) as an alternative threshold estimation technique to minimize the required trial count without predetermined knowledge of the relevant stimulus space. The directional acuity threshold was estimated at 11.7 ± 3.8° from the PEST method (n = 11 of 25 subjects, psychometric threshold = 10.1 ± 3.1°) using only one-third the number of trials compared to the psychometric method. Furthermore, PEST estimates of the direction acuity threshold were highly correlated with the psychometric estimates across subjects (r = 0.93) suggesting that both methods provide comparable estimates of the perceptual threshold. Computational modeling of both techniques revealed similar variance in the estimated thresholds across simulations of about 1°. Our results suggest that the PEST algorithm can be used to more quickly quantify whole-body directional acuity during standing in individuals with balance impairments.
M. J. Puntkattalee, C. J. Whitmire, A. S. Macklin, G. B. Stanley, L. H. Ting. Directional Acuity of Whole-Body Perturbations during Standing Balance, Gait & Posture 48, 77-82, 2016. PDF