Experiments described in a new paper used an impressive array of techniques to look at neuron activity in the whisker sensory cerebral cortex in awake mice performing an active tactile object localization task.
The authors of “Neural Activity in Barrel Cortex Underlying Vibrissa-Based Object Localization in Mice” published September 23, 2010 in Neuron asked “what information individual barrel cortex neurons might provide about object location.” A barrel in the cerebral cortex is the area receiving robust input from a single identified whisker (technically a vibrissa) on the rodent’s snout.
Using loose-seal cell-attached patch-clamping and two-photon imaging they found the following:
- Some neurons discriminated trial types nearly perfectly
- Over half of all neurons did not discriminate above chance levels
- Discrimination performance depended on the overall spike rate of the neuron and on cortical layer
The assumption they make is that discrimination is based on an absolute rate increase significantly above baseline.
The research team observed dramatic differences among cortical layers in overall spike rates and in the degree to which neurons of different layers carried information about the trial type. For instance, neurons in layers 2 and 3 showed sparse and low activity. Neurons in these layers sometimes showed a high degree of discrimination. Neurons in layer 6 showed low activity or ability to discriminate. In contrast Layer 4 and Layer 5 neurons showed high activity with relatively numerous neurons showing a high degree of discrimination.
The results of this study are intriguing. I particularly find the intracortical layer-by-layer differences fascinating. Nevertheless, I’m left with the sense that we remain a long way from actually understanding the original question “what information individual barrel cortex neurons might provide about object location.”
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