"Attentional state modulation of neural responses in rat auditory cortex"

Gonzalo H. Otazu, Anthony M. Zador


Primary auditory cortex is involved in the representation of auditory information. However, an animal's attentional state can also affect the neural representation of a stimulus. Here we have studied the neural correlates of modulation during a simple attentional task.

We compared neural responses recorded while animals were performing a two-alternative choice auditory task ("attending condition") to those recorded while the animal was awake, but not engaged in any task ("non-attending condition").  We implanted tetrodes to allow chronic recordings in rat auditory cortex. We delivered auditory stimuli through earphones in the unrestrained animal, allowing us to measure cortical responses to identical acoustic stimuli while the animal was free to move.

We observed that the multiunit activity evoked responses were consistently larger in the non-attending condition than in the attending condition. There was no change in the spontaneous activity, and the effect could also be observed at the level of the local field potential (LFP).

We also recorded in the medial geniculate body of the thalamus of animals performing the same task. We did not observe a difference in the evoked responses between the attending condition compared with the non-attending condition. However, we did observe an increase in the spontaneous activity while the animal was performing the task.  This increase is consistent with a model in which the elevated spontaneous firing rate in thalamus depresses the thalamic-cortical synapses, reducing the effects of acoustical stimulation on the engaged auditory cortex.