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Early sensory pathways for detection of fearful conditioned stimuli: tectal and thalamic relays
Journal article   Open access   Peer reviewed

Early sensory pathways for detection of fearful conditioned stimuli: tectal and thalamic relays

Jeremy D Cohen and Manuel A Castro-Alamancos
The Journal of neuroscience, v 27(29), pp 7762-7776
18 Jul 2007
PMID: 17634370
url
https://doi.org/10.1523/JNEUROSCI.1124-07.2007View
Published, Version of Record (VoR) Open

Abstract

Tetrodotoxin Electric Stimulation - adverse effects Evoked Potentials - radiation effects Rats, Long-Evans Rats Superior Colliculi - physiology Male Avoidance Learning - physiology Functional Laterality Nerve Block - methods Conditioning, Classical - physiology Rats, Sprague-Dawley Thalamus - injuries Kainic Acid Behavior, Animal Fear Animals Vibrissae - physiology Afferent Pathways - injuries Thalamus - physiology Afferent Pathways - physiology Acoustic Stimulation - adverse effects Vibrissae - innervation Superior Colliculi - injuries
Sensory stimuli acquire significance through learning. A neutral sensory stimulus can become a fearful conditioned stimulus (CS) through conditioning. Here we report that the sensory pathways used to detect the CS depend on the conditioning paradigm. Animals trained to detect an electrical somatosensory stimulus delivered to the whisker pad in an active avoidance task were able to detect this CS and perform the task when a reversible or irreversible lesion was placed in either the somatosensory thalamus or the superior colliculus contralateral to the CS. However, simultaneous lesions of the somatosensory thalamus and superior colliculus contralateral to the CS blocked performance in the active avoidance task. In contrast, a lesion only of the somatosensory thalamus contralateral to the same CS, but not of the superior colliculus, blocked performance in a pavlovian fear conditioning task. In conclusion, during pavlovian fear conditioning, which is a situation in which the aversive outcome is not contingent on the behavior of the animal, the sensory thalamus is a critical relay for the detection of the CS. During active avoidance conditioning, a situation in which the aversive outcome is contingent on the behavior of the animal (i.e., the animal can avoid the aversive event), the sensory thalamus and the superior colliculus function as alternative routes for CS detection. Thus, even from early stages of sensory processing, the neural signals representing a CS are highly distributed in parallel and redundant sensory circuits, each of which can accomplish CS detection effectively depending on the conditioned behavior.

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