Midbrain structures controlling vocalization in the domestic chick.

Area of Science:

• Neuroscience
• Animal Behavior
• Avian Vocalization

Background:

• The anterior intercollicular area (ICo) is implicated in vocalization control in birds.
• Previous studies suggest a role for the ICo in auditory processing and motor output for calls.

Purpose of the Study:

• To investigate the role of the anterior intercollicular area (ICo) in vocalization control in domestic chicks.
• To determine the effects of specific ICo lesions on different types of vocalizations and their evocation.
• To explore potential neural pathways involved in vocalization and their relation to the ICo.

Main Methods:

• Surgical creation of bilateral lesions confined to the anterior intercollicular area (ICo) in domestic chicks.
• Behavioral testing in open field and response to novel stimuli to assess vocalization.
• Analysis of calling behavior, including latency and evocation by specific stimuli.
• Investigation of vocalizations following partial ICo destruction and combined lesions ventral to the ICo.
• Assessment of crowing behavior and vocalizations in totally deafened birds.

Main Results:

• Bilateral ICo lesions resulted in complete muting, with loss of calling in open field tests and to novel stimuli.
• Lesions of the medial edge of the ICo also caused muting, potentially by disrupting connections with the central mesencephalic gray.
• Partial ICo destruction led to normal intensity calling but with significantly increased latency.
• Destruction of an area ventral to the ICo, along with partial ICo damage, resulted in the reappearance of a specific type of calling, often associated with locomotion.
• Crowing behavior was preserved after ICo lesions, suggesting alternative neural pathways.
• Vocalization in totally deaf birds remained normal, ruling out hearing deficits as the cause of ICo-induced muting.

Conclusions:

• The anterior intercollicular area (ICo) plays a critical role in the normal production and evocation of vocalizations in domestic chicks.
• Specific subregions and connections of the ICo are essential for different aspects of vocal control, including call initiation and response to stimuli.
• Alternative neural pathways exist for certain vocalizations, such as crowing, that bypass the ICo.
• The findings provide insights into the neural circuitry of vocalization and identify potential mammalian homologues of the ICo and its connections.