Eyeblink conditioning using cochlear nucleus stimulation as a conditioned stimulus in developing rats.

Area of Science:

• Neuroscience
• Developmental Psychology
• Behavioral Neuroscience

Background:

• Auditory conditioned stimulus (CS) input to the cerebellum is implicated in the emergence of eyeblink conditioning.
• The ontogeny of this conditioning may involve developmental changes in neural pathways, particularly those originating from the cochlear nucleus (CN).

Purpose of the Study:

• To investigate the role of developmental changes in cochlear nucleus (CN) projections in the ontogeny of auditory eyeblink conditioning.
• To determine if electrical stimulation of the CN as a conditioned stimulus (CS) can elicit eyeblink responses in developing rats.

Main Methods:

• Rat pups were implanted with electrodes in the CN and received paired training with CN stimulation (CS) and periorbital shock (US) on postnatal days (P) 17-18 or 24-25.
• Control groups received unpaired presentations of the CS and US.
• Conditioning was assessed by measuring eyeblink conditioned responses; electrode placement was verified post-mortem.

Main Results:

• Rats receiving paired training in both age groups demonstrated significant increases in eyeblink conditioned responses compared to unpaired controls.
• Rats trained at P24-25 exhibited stronger conditioning than those trained at P17-18.
• Rats with misplaced electrodes in the inferior cerebellar peduncle or cerebellar cortex did not show conditioning.

Conclusions:

• Developmental changes in CN projections to auditory and cerebellar pathways are critical for the ontogeny of auditory eyeblink conditioning.
• The maturation of these projections between P17-18 and P24-25 contributes to enhanced conditioning efficacy.
• These findings highlight the CN's role in the developmental emergence of associative learning.