Causal role of auditory cortex in mediating attention to moments in time

Abstract

Event Abstract Back to Event Causal role of auditory cortex in mediating attention to moments in time Attention is the means by which the brain selects and highlights important sensory information for further processing, ignoring or suppressing the rest. The earliest single unit studies revealed that neural activity in the first stages of cortical sensory processing is modulated by attention (Hubel et al., 1959). To date, most of what is known about the neural mechanisms underlying attention is based on correlations between neural activity and behavior. Here we establish for the first time that not only is neural activity in the auditory cortex correlated with attention, but that the auditory cortex is causally involved in mediating the behavioral advantages conferred by attention. We first developed a rodent behavioral paradigm in which we could demonstrate that attention enhanced performance on a sensory discrimination task. The task was an auditory two-alternative choice paradigm, modeled after a related visual paradigm in humans (Coull and Nobre, 1998), in which we manipulated attention to moments in time. Rats were required to detect a frequency-modulated target sound immersed in a train of pure tone distractors. Performance varied systematically with task difficulty, manipulated by the varying modulation depth of the target. Behavioral analysis showed a clear improvement in both reaction times and correct discrimination whenever the target appeared at an expected moment, compared to the same target appearing unexpectedly. These results show that attention improved performance. We next used tetrodes to record responses from single neurons in the primary auditory cortex of rats performing this task. The majority of responsive neurons showed an increase evoked response to tones immediately preceding the expected appearance of the target when compared against responses to the same tones occurring long before the expected target location. These results show that attention to moments in time modulates changes in neural activity in the auditory cortex. Finally, we assessed the effect on performance of pharmacological inactivation of the auditory cortex. We used the GABA-A receptor agonist muscimol to reversibly inactivate the auditory cortex bilaterally. Muscimol inactivation impaired performance compared with control application of saline, implying that the auditory cortex plays an important role in this task under normal conditions. Furthermore, inactivation of the auditory cortex significantly reduced the improvements in performance associated with attention. These results suggest that the auditory cortex is required to mediate the behavioral advantage conferred by attention. In summary, we have shown that: (1) attention to moments in time can lead to improved performance on a two-alternative choice auditory detection/discrimination task in rats; (2) neural activity in the primary auditory cortex is correlated with attention to moments in time; and (3) the auditory cortex plays a causal role in mediating the behavioral advantage conferred by attention.