The supragenual nucleus: A putative relay station for ascending vestibular signs to head direction cells

Lesions of the Tegmentomammillary Circuit in the Head Direction System Disrupt the Head Direction Signal in the Anterior Thalamus

“…Many DTN neurons exhibit sensitivity to AHV (Bassett and Taube, 2001;Sharp et al, 2001b), as do a subpopulation of LMN neurons (Stackman and Taube, 1998). Thus, an intriguing possibility is that the anomalous AHV sensitivity seen here represents the unmasking of velocity information conveyed to the ADN or LMN from a source not previously proposed (e.g., the supragenual nucleus) (Biazoli et al, 2006) (Fig. 1).…”

“…In the case of a unilateral lesion (left DTN; gray shading), only information reaching the right DTN from the contralateral supragenual nucleus and ipsilateral nucleus prepositus hypoglossi can reach either ADN via the LMN (lost connections shown as dotted lines). AHV input might still reach the left LMN via a direct projection from the supragenual nucleus (Biazoli et al, 2006). MVN, Medial vestibular nucleus; NPH, nucleus prepositus hypoglossi; PoS, postsubiculum; RSC, retrosplenial cortex; SGN, supragenual nucleus.…”

“…Some animals sustained lesser damage to these same areas: (1) two animals sustained partial damage (Ͻ40%) to the medial longitudinal fasciculus (Table 1, rats 76 and 153), (2) one animal had a unilateral lesion of the ventral tegmental nuclei (Table 1, rat 76), and (3) one animal had an incomplete lesion (Ͻ60%) of the laterodorsal tegmental nucleus (Table 1, rat 80). In no case was the supragenual nucleus, which is intimately connected with areas in the HD cell circuitry (Biazoli et al, 2006), involved in the lesion area. Figure 3A shows a representative example of a complete lesion, and Figure 3, B and C, shows an example of recording electrode tracks through the ADN of the same animal.…”

“…The LMN projects to the ADN bilaterally, but neither the ADN nor LMN have commissural projections to their contralateral counterparts. Therefore, activity recorded in the ADN can only reflect bilateral vestibular input with both DTNs intact, although Biazoli et al (2006) have recently reported direct projections from the supragenual nucleus to the LMN, which may constitute a distinct entry for head velocity information into the HD circuit. The anatomical connections described here are summarized in Figure 1.…”

The neural correlates of navigation beyond the hippocampus

“…Each of these areas receives direct projections from the medial vestibular nucleus. Both the NPH and PGRNd project to the SGN, and both the NPH and SGN have reciprocal connections with the DTN (Biazoli et al, 2006;Brown et al, 2005;Iwasaki et al, 1999;McCrea and Baker, 1985). In addition, the SGN also projects directly to LMN, which is reciprocally connected with DTN (Allen and Hopkins, 1989;Bassett et al, 2007;Zyo, 1990, 1992).…”