Figure 1.

Schematic diagram showing the principle connections in the HD cell circuit as well as a proposed model of information flow (Sharp et al., 2001a; Taube and Bassett, 2003). Arrows represent direction of information flow between connected areas. Black arrows represent excitatory connections, whereas the broken line depicts inhibitory connections. The DTN receives inputs from the nucleus prepositus, supragenual nucleus, and the IPN. The nucleus prepositus and supragenual nucleus both receive inputs from the medial vestibular nuclei, whereas the IPN receives inputs predominantly from the medial and lateral habenula. It has been proposed that IPN inputs into the DTN might be a source of motor input (Taube, 2007), which together with the vestibular information relayed from the nucleus prepositus and supragenual nucleus represent multiple idiothetic pathways of information about self-movement projecting into the HD circuit. Previous studies suggest that the projections from the postsubiculum to the ADN and LMN constitute an allothetic pathway in which visual information enters the HD cell system (Goodridge and Taube, 1997). Finally, the connections between the DTN and LMN appear to be central to the generation of HD cell activity. LH, Lateral habenula; MH, medial habenula; MVN, medial vestibular nuclei; NPH, nucleus prepositus; PoS, postsubiculum; SGN, supragenual nucleus.