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Changes in visual responsiveness following intercollicular lesions and their effects on avoidance and attack
Abstract:
In the normal chick, conspicuous visual stimuli induce targetting and pecking together, with vocalization. All three are abolished by lesion of the intercollicular area (ICo) or of connections passing through its medial margin. After such lesions, chicks also cease to treat significant visual stimuli as if they were startling and exciting, and may delay response as a result. However, they are still able to recognise, orient accurately to, and respond appropriately to, a variety of complex visual stimuli (e.g. food grains, copulation object). In addition, they are little affected by strange surroundings. Lesion evidence suggests the mammalian subcollicular area to have similar functions to the ICo and to be homologous with it. A route (present in bird), which is well-known in mammals for its association with threat, defense and escape evoked by strange and frightening objects (amygdala-diencephalic periventricular system-central mesencephalic grey, A-DPS-CMG) is stimuli via the 2 ICo (subcollicular area). Two different mechanisms may be involved caudal to the ICo. One consists of tectal afferents which might modulate the evocation of targetting, pecking and other responses via the tectum. The other is the predorsal system of tectal efferents which may mediate such responses. Classical syndromes of tameness and unresponsiveness produced by various interruptions of the A-DPS-CMG route may depend on interruption of connections to these midbrain mechanisms. Attack is depressed by ICo lesions as one aspect of reduced responsiveness to conspicuous and startling visual stimuli. Avoidance, which is apparently mediated by a separate system, much as in Anura, is facilitated.
Insights
Lesioning the intercollicular area (ICo) in chicks disrupts visual startle responses and attack behaviors. However, chicks retain the ability to recognize and respond to complex visual stimuli, suggesting distinct neural pathways for different visual processing.
Area of Science:
- Neuroscience
- Animal Behavior
- Comparative Neurology
Background:
- Conspicuous visual stimuli normally elicit targetting, pecking, and vocalization in chicks.
- The intercollicular area (ICo) and its connections are crucial for these responses.
- Lesions to the ICo abolish these responses and alter the perception of startling visual stimuli.
Purpose of the Study:
- To investigate the role of the intercollicular area (ICo) in visual processing and behavioral responses in chicks.
- To explore the homologous functions of the mammalian subcollicular area.
- To elucidate the neural pathways involved in threat detection and avoidance.
Main Methods:
- Lesion studies in chicks targeting the intercollicular area (ICo).
- Observation and analysis of behavioral responses to various visual stimuli (e.g., food, conspecifics, novel objects).
- Comparative analysis with mammalian neural structures like the amygdala-diencephalic periventricular system-central mesencephalic grey (A-DPS-CMG) pathway.
Main Results:
- ICo lesions abolished targetting, pecking, and vocalization in response to conspicuous visual stimuli.
- Chicks with ICo lesions showed reduced startle responses and delayed reactions to significant visual stimuli.
- Despite deficits, lesioned chicks could still recognize, orient to, and appropriately respond to complex visual stimuli like food and a copulation object.
- Lesions did not significantly affect responses to novel surroundings.
- Mammalian subcollicular area appears homologous to the avian ICo.
- Attack behavior was depressed by ICo lesions, while avoidance behavior was facilitated, suggesting separate neural mediation.
Conclusions:
- The intercollicular area (ICo) plays a critical role in mediating startle, targetting, and attack behaviors in response to conspicuous visual stimuli.
- Separate neural mechanisms, potentially involving tectal afferents and efferents, are involved in modulating and mediating these responses caudal to the ICo.
- The amygdala-diencephalic periventricular system-central mesencephalic grey (A-DPS-CMG) pathway's role in threat and defense may be linked to its connections with these midbrain mechanisms.
- Avoidance behavior is mediated by a distinct system, similar to that observed in Anura.
