Role of the Dorsal Cortex of the Inferior Colliculus in the Precedence Effect.

BACKGROUND The precedence effect (PE) is a physiological phenomenon for accurate sound localization in a reverberant environment. Physiological studies of PE have mostly focused on the central nucleus of the inferior colliculus (CNIC), which receives ascending and descending projections, as well as projections from the shell of the inferior colliculus (IC) and contralateral IC. However, the role of the dorsal cortex of the IC (DCIC), which receives ascending and descending projections to ensure sound information processing and conduction on PE formation, remains unclear. Therefore, this study aimed to understand the role, if any, of the DCIC on PE formation in male Sprague Dawley rats. MATERIAL AND METHODS In vivo, 16-channel electrophysiological recordings were performed in anesthetized rats to investigate neuronal responses in the CNIC, after inducing electrolytic lesions in the DCIC. In vitro, the expression of inhibitory gamma-aminobutyric acid (GABA)ergic receptors in the CNIC was analyzed by Western blot. RESULTS After inducing electrolytic lesions in the DCIC, normalized neural responses of the CNIC to lagging stimuli were significantly increased (P<0.05), half-maximal inter-stimuli delays were shortened (P<0.05), and the expression of GABA A receptor a1 and GABA B receptor 2 decreased (P<0.05). Furthermore, neurons in the CNIC showed a contralateral preference when paired sounds in the free field were presented. CONCLUSIONS Our study suggests that the DCIC could modulate PE formation in the CNIC, potentially involving inhibitory GABAergic mechanisms. This study showed the role of the DCIC on PE formation and proposed a potential structure for identifying likely mechanisms of the PE in the IC.