Long-Evans rat pups, 17-18 or 24 days of age, were trained with an eyeblink conditioning (EBC) procedure that was used previously with adult rats (Skelton, 1988). Pups received 3 sessions of delay conditioning in a single day at about 4-hr intervals (100 trials/session). Trials involved pairings of an auditory conditioned stimulus (2.8-kHz, 82-dB tone) and a periocular-shock unconditioned stimulus (US; 100 ms, 2 mA), which were presented 280 ms apart. EBC was observed at both ages, but older pups learned much more rapidly. Subsequent experiments established that this effect is associative (Experiment 2), that age differences in EBC cannot be attributed to differences in ability to respond or in sensitivity to the US (Experiment 3), and that EBC rate can be modulated by motivational state (Experiment 4). This preparation may help elucidate the relation between neural development and the ontogeny of learning.

No abstract

Electromyographic eyelid responses in unrestrained rats were classically conditioned in a Pavlovian delay paradigm by using a tone conditioned stimulus (CS) and periorbital shock unconditioned stimulus (US). After eyelid conditioning was complete, bilateral electrolytic lesions were made in the dentate-interpositus region of the cerebellar nuclei. Initial eyelid conditioning was reliable and very similar to that previously observed in the rabbit, although the asymptotic eyelid responses contained a short-latency startle response in addition to the usual conditioned and unconditioned responses (CR and UR). Substantial decrements in CRs were observed in 13 of the 14 rats with accurately placed lesions. In contrast, startle responses and URs were unaffected. The results replicate the effects of cerebellar lesions on eyelid CRs in the rabbit and suggest that the anatomical basis of eyelid conditioning in both species is similar.

Rats lever pressed for concurrent electrical stimulation of the lateral hypothalamus and ventral tegmentum. The pulse-pair stimulation technique was used, with the first pulse of each pair applied to one electrode and the second to the other electrode; the intrapair interval was varied. The effectiveness of stimulation, measured behaviorally, increased abruptly (within .4 msec) as the intrapair interval was increased in the range from 1.0 to 2.0 msec These results, which do not resemble single-electrode refractory period results, are interpreted as evidence of collision in the directly stimulated, reward-related neurons linking the two sites. We conclude that self-stimulation of the medial forebrain bundle involves the direct activation of long-axon, longitudinal pathways. Estimates of the conduction velocity in the fibers subserving the collision-like effects are consistent with the properties of small myelinated axons but not central monoaminergic fibers.

Spatial learning and memory has been linked to the hippocampus and temporal lobes and though these areas are often damaged in traumatic brain injury (TBI), spatial learning deficits after TBI have not received much attention. In the present study, a virtual environment was used to challenge people with TBI to solve a task comparable to the Morris water maze, which in turn has been shown to be highly sensitive to hippocampal and frontal lobe dysfunction in laboratory animals. A regular computer monitor was used to present 12 participants with TBI and 12 age- and sex-matched comparison participants with a computer-generated, three-dimensional "virtual arena maze," consisting of a large round arena within a very large square room. Participants were required to learn the place of an invisible target on the floor of the room based solely on distal cues on the walls of the room. Eight of the 12 participants with moderate to severe TBI showed substantial place-learning deficits in comparison to the uninjured participants. Performance in the virtual environment correlated with self-reported frequency of wayfinding problems in everyday life and with scores on a test of episodic memory, the Rivermead Behavioural Memory Task. These data confirm that deficits in spatial learning and memory follow TBI, and suggest that the virtual arena maze may provide a new method for objectively assessing them.