Date on Master's Thesis/Doctoral Dissertation
Anatomical Sciences and Neurobiology
Anatomical Sciences and Neurobiology, PhD
Committee Co-Chair (if applicable)
thalamus; anatomy; electrophysiology; consummatory behavior; odor-taste mixtures
The mediodorsal thalamus (MD) is thought to be key component of the network that processes chemosensory information to guide our consummatory choices. Previous studies show that the mediodorsal thalamus receives projections from both the piriform cortex (PC) and gustatory cortex (GC), suggesting that it may process chemosensory information from both areas. Although the mediodorsal thalamus has been shown to respond to odors detected by sniffing, it remains unknown how its neurons represent experienced odors, tastes, and odor-taste mixtures originating from the mouth. Importantly, humans and animals with mediodorsal thalamic lesions do not suffer from anosmia, but experience deficits in odor attention, and the hedonic perceptions of odors and odor-taste mixtures. To gain a better understanding of the role of the mediodorsal thalamus in processing chemosensory information, my dissertation project focused on investigating its connectivity, physiology, and behavioral relevance in the context of consummatory choice. I used an intersectional viral approach and found that a greater proportion of neurons in the mediodorsal thalamus form cortico-thalamic connections with the gustatory cortex than with the posterior piriform cortex. This result suggests that input from the gustatory cortex may more broadly influence processing in the mediodorsal thalamus than the posterior piriform cortex. Next, I recorded responses of neurons in the mediodorsal thalamus to experienced odors, tastes, and odor-taste mixtures delivered into the mouth. I found that neurons in the mediodorsal thalamus encode the identity of individual odors, tastes, and odor-taste mixtures. Additionally, subpopulations of neurons represent taste palatability and represent odor-taste mixtures differently than their odor or taste component. These results are the first to show the mediodorsal thalamus encodes taste and odor-taste information. Finally, I used pharmacological inactivation during a two-bottle brief-access task to determine the role of the mediodorsal thalamus in the consummatory choice. I found that inactivation of the mediodorsal thalamus decreases overall consumption and increases the amount of switching between two stimuli, suggesting its importance in sensory attention and stimulus value during consummatory choice tasks. Taken together, these data indicate that the mediodorsal thalamus is important to the network that processes chemosensory signals and informs consummatory choice.
Fredericksen, Kelly, "Chemosensory processing by the mediodorsal thalamus." (2023). Electronic Theses and Dissertations. Paper 4075.