Functional MRI of Eyeblink Conditioning in the Rabbit.

Classical conditioning has been well studied over the last century as a method for investigating learning and memory. The rabbit eyeblink response is commonly used as a basis for such studies, and combined with lesions or electrophysiological recordings has provided a well-controlled paradigm for investigating the neurobiological mechanisms underlying learning and memory. However, these methods are invasive, examine only restricted portions of the circuit at one time, and require many animals for a thorough analysis. More recently functional imaging techniques have enabled the simultaneous, noninvasive examination of the entire brain. Functional MRI (fMRI), in particular, is characterized by superior spatial and temporal resolution and is suitable for repeated application. The application of fMRI to imaging eyeblink conditioning in animals would be desirable, as it would allow a more direct comparison to previous results from animal studies, and could potentially utilize methods such as electrode recordings or the application of drugs, which would not be possible in humans. However, the difficulty of acquiring reliable functional images from unanesthetized animal subjects over the course of multiple experiments has proved a major barrier to implementing a successful animal model for studies such as eyeblink conditioning that require awake, behaving subjects. This thesis describes the development of a systematic methodology to enable the reliable acquisition of fMRI data during eyeblink conditioning in rabbits, and the application of this methodology to imaging functional activity in key brain regions during eyeblink conditioning. Issues including animal preparation, eyeblink measurement, the avoidance of eyeblink-related artifacts, and fMRI data processing and analysis are discussed. fMRI results are presented from delay eyeblink conditioning in the cerebellum, as well as from a direct comparison of delay and trace conditioning in the primary sensory cortices, caudate nucleus, and hippocampus. These regions have previously demonstrated involvement in learning, and we observed the presence of both learning-related plasticity and distinct differences in the patterns of functional changes between delay and trace paradigms. This work represents the first successful application of fMRI to imaging learning-related functional changes in an animal model, and the first fMRI study to compare directly delay and trace eyeblink conditioning.