Behavioral role of the mammillary efferent system

Lesions of the mammillothalamic tract impair the acquisition of spatial but not nonspatial contextual conditional discriminations

“…Therefore, lesions of this tract might provide a unique insight into the functional significance of the circuit; in particular, such lesions could reveal the contribution of the interaction between the mammillary bodies and anterior thalamic nuclei. Previous studies have shown that MTT lesions result in a pattern of deficits (in a variety of maze‐based tasks) that is indicative of an impairment in the encoding of spatial information (Field et al ., 1978; Thomas & Gash, 1985; Vann & Aggleton, 2003). Here, we sought more direct evidence that MTT lesions result in a deficit in encoding spatial information.…”

“…The finding that MTT lesions result in an initial impairment in learning a visuo‐spatial contextual discrimination is consistent with studies showing that rats with MTT lesions are impaired on a variety of spatial tasks (Krieckhaus & Randall, 1968; Field et al ., 1978; Thomas & Gash, 1985; Vann & Aggleton, 2003), but appear inconsistent with at least two other studies (Gabriel et al ., 1995; Sziklas et al ., 1996). In one of these studies, rats with mammillary body lesions were unimpaired in learning a conditional discrimination with a clear spatial component (Sziklas et al ., 1996).…”

Hippocampal, retrosplenial, and prefrontal hypoactivity in a model of diencephalic amnesia: Evidence towards an interdependent subcortical‐cortical memory network

“…A third hypothesis combines the previous two hypotheses by proposing that diencephalic damage causes widespread cortical dysfunction, again due to a loss of hippocampal inputs, and this is responsible for subsequent memory impairment (Mair et al, 1979;Paller, 1997;Vann and Aggleton, 2004). These three hypotheses can all accommodate the finding that MTT lesions impair spatial tasks that depend on the integrity of the hippocampus and anterior thalamic nuclei (Field et al, 1978;Vann and Aggleton et al, 2003) and all emphasize the importance of hippocampal inputs to the medial diencephalon. However, because the hippocampus also directly projects to both the prefrontal cortex and cingulate cortex, the mammillary bodies and/or anterior thalamus would need to provide additional information or these indirect pathways would seem redundant.…”

The dorsal premammillary nucleus: an unusual component of the mammillary body.

“…And while the input/output relationships of the medial zone are complex, the nuclei are dominated by afferents from limbic regions ofthe telencephalon that clearly divide them into two groups: caudal (mammillary) and rostral. The mammillary group receives a major input from the postcommissural fornix, which arises in the subicular complex of the hippocampal formation (2)(3)(4)(5) and is a major component of the classical "Papez circuit" (6), which is now thought to play a role in learning and memory (7)(8)(9)(10). In contrast, the rostral group of medial zone nuclei receives massive inputs from the amygdala (11), ventral subiculum (3,11), and lateral septal nucleus (12) that are dominated by olfactory information and play a role in expression of ingestive and reproductive behaviors (1).…”