Abstract
The medial diencephalon, in particular the mammillary bodies and anterior thalamic nuclei, has long been linked to memory and amnesia. The mammillary bodies provide a dense input into the anterior thalamic nuclei, via the mammillothalamic tract. In both animal models, and in patients, lesions of the mammillary bodies, mammillothalamic tract and anterior thalamic nuclei all produce severe impairments in temporal and contextual memory, yet it is uncertain why these regions are critical. Mounting evidence from electrophysiological and neural imaging studies suggests that mammillothalamic projections exercise considerable distal influence over thalamo-cortical and hippocampo-cortical interactions. Here, we outline how damage to the mammillary body-anterior thalamic axis, in both patients and animal models, disrupts behavioural performance on tasks that relate to contextual (“where”) and temporal (“when”) processing. Focusing on the medial mammillary nuclei as a possible ‘theta-generator’ (through their interconnections with the ventral tegmental nucleus of Gudden) we discuss how the mammillary body-anterior thalamic pathway may contribute to the mechanisms via which the hippocampus and neocortex encode representations of experience.
Highlights
Memory is thought to arise from the integration of multiple pro cessing streams subserved by several anatomical brain circuits
While the importance of the mammillary bodies (MBs) and anterior thalamic nuclei (ATN) for contextual memory has been repeatedly demonstrated, there are still many outstanding questions in terms of what these impairments reflect. Is it impoverished contextual encoding? an impairment in combining features? or perhaps both? The behavioural tests typically used in animals require integrated learning, e.g. combining reward, shock, an object, or an odour with context, making it difficult to tease apart the underlying impairment
Resolving this issue may depend on electrophysiological recordings, rather than behaviour alone, which would enable context-related neural signatures to be assessed in intact animals and following the disruption of medial MB-ATN connections
Summary
Memory is thought to arise from the integration of multiple pro cessing streams subserved by several anatomical brain circuits. Neuroscience and Biobehavioral Reviews 121 (2021) 60–74 considered to be merely a part of an ’extended hippocampal system’ whose main function was to relay hippocampal signals to the cortex While this model accurately reflects connectivity of the major anatom ical pathways (including subicular inputs to the MBs via the fornix, MB projections to the ATN via the MTT and, ATN efferents to both the hippocampus and the neocortex; see Fig. 1), it does not account for. The MBs receive a number of extra-hippocampal afferents (including the tegmental nuclei of Gudden, medial septum and supra mammillary nucleus) which again suggests they process more diverse information streams This idea is further supported by behavioural ev idence as disconnection of hippocampal inputs to the MBs fails to pro duce deficits as severe as those following MB or MTT lesions (Roy et al, 2017; Tonkiss and Rawlins, 1992; Vann, 2013; Vann et al, 2011) rein forcing the importance of these non-hippocampal inputs.
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
