Lesions to the lateral mammillary nuclei disrupt spatial learning in rats.

Abstract

The head direction (HD) signal is thought to originate in the reciprocal connections between the dorsal tegmental nuclei (DTN) and the lateral mammillary nuclei (LMN) and lesions to these structures disrupt the HD signal in downstream structures. Lesions to the DTN also disrupt performance on spatial tasks where directional heading is thought to be important. In Experiment 1, rats with bilateral electrolytic lesions of the LMN and sham controls were trained on 2 tasks previously shown to be sensitive to DTN damage. Rats were first trained on either a direction or rotation problem in a water maze. LMN-lesioned rats were impaired relative to sham controls, on both the first block of 8 trials and on the total number of trials taken to reach criterion. In the food-foraging task, rats were trained to leave a home cage at the periphery of a circular table, find food in a food cup at the center of the table, and return to the home cage. Again, LMN-lesioned rats were impaired relative to sham rats, making more errors on the return component of the foraging trip. In Experiment 2, rats with electrolytic LMN lesions were also impaired on a dry land version of the direction and rotation problems and had difficulty discriminating between reinforced and nonreinforced locations on a 12-arm maze. These results build on previous behavioral and cell-recording studies and demonstrate the importance of the direction system to spatial learning.

Contextual experience modifies functional connectome indices of topological strength and efficiency

“…Undersampled Nyquist frequencies can alias into the measured fMRI signal and drive hypothalamic 'synchronous' activity in the presence of suppressed cortical connectivity strength. However, despite this possible non-neuronal mechanism there are studies that have observed a role for hypothalamic nuclei in functional connectivity in models of pain, in human studies of migraine headache, and in studies of obesity where increases in hypothalamic functional connectivity have been reported [62][63][64] .…”

Contextual experience modifies functional connectome indices of topological strength and organization

“…Nyquist frequencies can alias into the measured fMRI signal and drive hypothalamic 'synchronous' activity in the presence of suppressed cortical connectivity strength. However, despite this possible non-neuronal mechanism there are studies that have observed a role for hypothalamic nuclei in functional connectivity in models of pain, in human studies of migraine headache, and in studies of obesity where increases in hypothalamic functional connectivity have been reported (83)(84)(85).…”