Doctor of Philosophy, Miami University, 2008, Psychology

Rabbit eyeblink classical conditioning (EBCC) is a task widely used to understand the neurobiological correlates of associative learning and memory. The hippocampus has proven to be an important structure in acquiring the association between the conditioning stimuli and the development of conditioned responses. This study used a brain-computer interface to trigger conditioning trials in the presence (T+) or absence (T-) of a frequency component of the hippocampal field potential historically related to sensory processing and attention, termed theta. The presence of theta has been shown to facilitate learning in this task as well as accelerate learning related unit responses in the hippocampus, but the precise nature of its beneficial effect in hippocampal neurophysiology has yet to be determined. In this study, tetrodes were lowered into the dorsal hippocampus of four groups of rabbits including those who received paired or unpaired conditioning stimuli in both T+ and T- theta conditions. Specialized signal processing software compared the extracted data streams from each wire of the tetrode to separate the waveforms into single neuron responses. Each sorted neuron was then categorized according to its firing properties as pyramidal cells or one of the known types of interneurons that exist in the hippocampus. The individual units were analyzed for their relation to the pretrial period as well as for how they responded to the conditioning stimuli. Interneurons were highly correlated with hippocampal state used to trigger the trials, supporting the existence of interneurons that systematically vary with the ongoing theta activity. Interneuron responses to the conditioning stimuli were generally dependent on hippocampal state, demonstrating excitatory responses in T+ groups and suppression in T- groups. Pyramidal cells that demonstrated suppression to the conditioning stimuli were also more common in T- groups, while excitatory pyramidal cells were more related to ass (open full item for complete abstract)

Committee: Stephen Berry PhD (Advisor); Allan Pantle PhD (Committee Member); Dragana Ivkovich Claflin PhD (Committee Member); Kathleen Killian PhD (Committee Member) Subjects: Behaviorial Sciences; Physiological Psychology; Psychobiology; Psychology

Master of Arts, Miami University, 2013, Psychology

Hippocampal interneurons are a heterogeneous group with identifiable subtypes. The present study utilized tetrode recordings and a brain-computer interface (BCI) to examine response profiles of five interneuron types (axo-axonic, basket, bistratified, cholecystokinin-expressing, and oriens-lacunosum-moleculare cells) during trace eyeblink conditioning in the rabbit. The BCI initiated trials in the presence (T+) or absence (T-) of hippocampal theta, a methodology previously shown to affect learning rate. In various trial epochs, T+ axo-axonic and basket cells showed greater responses than those in T-, while T- oriens-lacunosum-moleculare cells showed greater responses than in T+. Such response profiles are consistent with models proposing a role for theta in storage vs. retrieval functions of the hippocampus. These data suggest theta modulation of distinct responses of interneuron subtypes, and support the idea that the naturally occurring theta rhythm can affect information processing by the hippocampus in ways that cause a significant improvement in behavioral learning rate.

Committee: Stephen Berry PhD (Committee Chair); Barbara Oswald PhD (Committee Member); Jennifer Quinn PhD (Committee Member) Subjects: Neurobiology; Psychobiology