Mammillothalamic disconnection alters hippocampo-cortical oscillatory activity and microstructure: Implications for diencephalic amnesia

Abstract

for technical, histological and surgical assistance. AbstractDiencephalic amnesia can be as disruptive as the more commonly known temporal lobe amnesia, yet the precise contribution of diencephalic structures to memory processes remains elusive. We used discrete lesions of the mammillothalamic tract to model aspects of diencephalic amnesia and assessed the impact of these lesions on multiple measures of activity and plasticity within the hippocampus and retrosplenial cortex. Lesions of the mammillothalamic tract had widespread indirect effects on hippocampo-cortical oscillatory activity within both theta and gamma bands. Both within-region oscillatory activity and cross-regional synchrony were altered. The network changes were state-dependent, displaying different profiles during locomotion and paradoxical sleep. Consistent with the associations between oscillatory activity and plasticity, complementary analyses using several convergent approaches revealed microstructural changes, which appeared to reflect a suppression of learning-induced plasticity in lesioned animals. Together, these combined findings suggest a mechanism by which damage to the medial diencephalon can impact upon learning and memory processes, highlighting important role for the mammillary bodies in the co-ordination of hippocampo-cortical activity.

Evidence for two distinct thalamocortical circuits in retrosplenial cortex

“…Consistent with previous work in freely moving animals, the LFP showed characteristic network patterns, including clear theta oscillations (Dillingham et al, 2019;Young and McNaughton, 2009;Borst et al, 1987;Talk et al, 2004). Theta oscillations from gRSC and dRSC did not differ in average peak Type-1 (movement-associated; Olvera-Cortés et al, 2002;Caplan et al, 2003) theta power and frequency (6-12 Hz; Fig.…”

Evidence for two distinct thalamocortical circuits in retrosplenial cortex

“…Consistent with previous work in freely moving animals, the LFP showed characteristic network patterns, including clear theta oscillations (Dillingham et al, 2019;Young and McNaughton, 2009;Borst et al, 1987;Talk et al, 2004). Theta oscillations from gRSC and dRSC did not differ in average peak Type-1 (movement-associated; Olvera-Cortés et al, 2002;Caplan et al, 2003) theta power and frequency (6-12Hz; Figure 2).…”

MRI measures of hypothalamic injury are associated with glucagon‐like peptide‐1 receptor agonist treatment response in people with hypothalamic obesity

“…B and C, box and whisker plots of hypothalamus or MB damage subscores by treatment group (horizontal line = median; box = interquartile range; whiskers = minimum and maximum). There was a statistically significant interaction between treatment and MB damage (p < .001) but not for posterior hypothalamus damage (p = .06 [32][33][34][35] In macaques, projections from the hippocampal formation to the posterior hypothalamus are confined to the medial and lateral MBs. 36 There is growing evidence that the hippocampus contributes to control of feeding behaviour, 13,37 perhaps modulated by MB inputs.…”

“…Finally, although there is currently little evidence to suggest a role of MBs in control of feeding behaviour or energy homeostasis, 31 our findings may indicate a role in modulating the neuronal circuitry underlying GLP‐1RAs and body fat regulation. The MBs are critically involved in learning and memory and are believed to serve as a hippocampal relay, to coordinate activity between the anterior thalamic nuclei and cingulate cortex 32–35 . In macaques, projections from the hippocampal formation to the posterior hypothalamus are confined to the medial and lateral MBs 36 .…”