Proceedings of The Physiological Society
Cardiff University (2009) Proc Physiol Soc 17, C06
Representation of temporal sensory features in the whisker thalamus
R. Petersen1, M. Bale1, A. Alenda2, M. Brambilla1, S. Panzeri3, M. Montemurro1, M. Maravall2
1. Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom. 2. Instituto de Neurociencias, UMH-CSIC, Alicante, Spain. 3. Italian Institute of Technology, Genoa, Italy.
The thalamo-cortical pathway is the crucial sensory gateway into the cerebral cortex. We aimed to determine both the nature of the tactile information encoded by neurons in the whisker somatosensory relay nucleus (VPm) and how it is encoded. We wanted to distinguish whether VPm neurons encode similar stimulus features, acting as a single information channel, or encode diverse features. We also wanted to determine whether stimulus features are encoded by the firing rate or by the precise timing of spikes. To address these issues, we recorded responses of single units in the rat VPm under urethane anaesthesia (i.p., 1.5 g (kg bodyweight)-1) to whisker deflections that thoroughly explored the space of temporal stimulus variables (for experimental details, see Montemurro et al., 2007). We then identified features to which neurons were selective by reverse correlation. We found that spikes were timed with sub-millisecond precision, and that this enabled neurons to convey a great deal of information (up to 77.9 bits/s) about whisker motion. To identify which sensory features these precisely timed spikes encode, we used a reverse correlation approach. We found that sensitivity to stimulus kinetics was surprisingly diverse. Some neurons (25%) only encoded velocity; others were sensitive to position, acceleration or more complex features. A minority (19%) encoded two or more features. These results indicate that VPm contains a distributed representation of whisker motion, based on high-resolution kinetic features.
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