Abstract
AbstractHow does attention modulate sensory representations? In order to probe the underlying neural mechanisms, we established a simple rodent model of modality-specific attention. Rats were trained to perform distinct auditory two-tone discrimination and olfactory odor discrimination in a two alternative choice (2AC) paradigm. To determine auditory cortex’s role in this frequency discrimination task, we used GABA-A receptor agonist muscimol to transiently and reversibly inactivate auditory cortexes bilaterally in rats performing simple interleaved auditory and olfactory discrimination. With olfactory discrimination performance serving as internal control for motivation and decision making capability, we found only auditory two-tone discrimination was selectively impaired in these rats. This shows the auditory cortex is involved in this two-tone discrimination task.To investigate the neural correlate of modality-specific attention in the auditory cortex, we trained rats to perform interleaved auditory and olfactory blocks (of 50~70 trials each) in a single session. In auditory blocks, pure tones were either presented with or without a neutral odor (caproic acid, n=2 and 3 respectively), and subjects were rewarded for discriminating auditory stimuli. In olfactory blocks, both task odors and pure tones were presented simultaneously, and subjects were rewarded for discriminating olfactory stimuli. We recorded neural responses in primary auditory cortex (area A1) in freely moving rats while subjects performed this behavior. Single unit responses to tones were heterogeneous, and included transient, sustained, and suppressed. We found 205 of 802 units recorded responsive to the stimuli we used. Of these 205 units, 18.5% showed modality-specific attentional modulation of the anticipatory activity before tone onset. In addition, we also observed in smaller proportion of units (11.2%) modality-specific attentional modulation of the tone-evoked responses; in most cases, the responses to a particular auditory stimulus was enhanced in the auditory block (or, equivalently, suppressed in the olfactory block). Attention increased choice probability of the population in the auditory block. We have also observed significant behavior choice probability in small proportions of units. Our results suggest that shifting attention between audition to olfaction tasks can modulate the activity of single neurons in primary auditory cortex.
Highlights
The ability to selectively process relevant sensory information depending on the animal’s internal state and to respond with appropriate action is essential to an animal’s survival
I have shown that the auditory cortex is involved in two-tone discrimination
I have developed and trained rodents to perform an auditory-olfactory intermodal selective attention task
Summary
The ability to selectively process relevant sensory information depending on the animal’s internal state and to respond with appropriate action is essential to an animal’s survival. Single-unit recordings from monkeys have provided evidence showing that attention modulates responses of auditory cortical neurons while the monkey is performing an intermodal selective attention task that uses combined auditory and visual stimuli. This modulation can affect even the earliest short-latency responses (Hocherman et al, 1976; Miller et al, 1980). Selective attention can either enhance or suppress the neuronal responses based on the relevant stimulus modality or whether stimuli in both modalities contradict each other (Hocherman et al, 1976) With this information in mind, I would like to extend our previous knowledge of intermodal selective attention to a well established rodent model, rats. Before the main body of the thesis, I’ll briefly review what we know from previous work about attentional modulation of neuronal activity in auditory cortex
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