Firing Properties of Rat Lateral Mammillary Single Units: Head Direction, Head Pitch, and Angular Head Velocity

Abstract

Many neurons in the rat anterodorsal thalamus (ADN) and postsubiculum (PoS) fire selectively when the rat points its head in a specific direction in the horizontal plane, independent of the animal's location and ongoing behavior. The lateral mammillary nuclei (LMN) are interconnected with both the ADN and PoS and, therefore, are in a pivotal position to influence ADN/PoS neurophysiology. To further understand how the head direction (HD) cell signal is generated, we recorded single neurons from the LMN of freely moving rats. The majority of cells discharged as a function of one of three types of spatial correlates: (1) directional heading, (2) head pitch, or (3) angular head velocity (AHV). LMN HD cells exhibited higher peak firing rates and greater range of directional firing than that of ADN and PoS HD cells. LMN HD cells were modulated by angular head velocity, turning direction, and anticipated the rat's future HD by a greater amount of time (approximately 95 msec) than that previously reported for ADN HD cells (approximately 25 msec). Most head pitch cells discharged when the rostrocaudal axis of the rat's head was orthogonal to the horizontal plane. Head pitch cell firing was independent of the rat's location, directional heading, and its body orientation (i.e., the cell discharged whenever the rat pointed its head up, whether standing on all four limbs or rearing). AHV cells were categorized as fast or slow AHV cells depending on whether their firing rate increased or decreased in proportion to angular head velocity. These data demonstrate that LMN neurons code direction and angular motion of the head in both horizontal and vertical planes and support the hypothesis that the LMN play an important role in processing both egocentric and allocentric spatial information.

Role of NeuroepithelialSonic hedgehogin Hypothalamic Patterning

“…The gap that is created in this way unexpectedly confirms neural plate fate-mapping data in zebrafish showing that the presumptive MAM is indeed caudal to, but not continuous with the rest of the hypothalamus (Staudt and Houart, 2007). This region has been considered a somewhat atypical part of the hypothalamus from the point of view of specification mechanisms (Mathieu et al, 2002), patterning (Puelles and Rubenstein, 2003), connectivity (Thompson and Swanson, 2003), and function (Stackman and Taube, 1998;Vann and Aggleton, 2004;Radyushkin et al, 2005).…”

A Continuous Attractor Network Model Without Recurrent Excitation: Maintenance and Integration in the Head Direction Cell System

“…From the neurophysiological point of view, the tuning curves we observe are quantitatively similar to the tuning curves recorded in the rat HD cell system. HD cells are numerous in the LMN (Blair et al, 1998;Stackman and Taube, 1998). In the DTN, the picture is less clear, because few electrophysiological recordings are available in this area Bassett and Taube, 2001b).…”

“…HD cells were first electrophysiologically recorded in the rat postsubiculum (PoSC) (Ranck, 1984;Taube et al, 1990a), and then found in numerous other structures including the laterodorsal thalamic nucleus (Mizumori and Williams, 1993), the dorsal striatum (Wiener, 1993), the retrosplenial cortex (Chen et al, 1994), the anterodorsal thalamic nucleus (ADN) (Taube, 1995;Blair and Sharp, 1995), the lateral mammillary nucleus (LMN) (Stackman and Taube, 1998), and the dorsal tegmental nucleus (DTN) .…”

“…A further evidence for the above processing pathway is provided by a series of studies that have investigated the temporal properties of HD cells in LMN, ADN, and PoSC. During head turns, LMN neurons tend to anticipate the future head direction by approximately 40-75 ms (Stackman and Taube, 1998;Blair et al, 1998), ADN cells show a smaller anticipatory time delay of about 25 ms (Taube and Muller, 1998;Cho and Sharp, 2001), and PoSC cells tend to encode the current directional heading (Blair and Sharp, 1995). The DTN-LMN circuit seems also well suited to account for the additional property of the HD cell system of integrating the head angular velocity.…”

Reconstruction of the postsubiculum head direction signal from neural ensembles

“…These cells have baseline-to-baseline tuning curve widths of 100° (Taube et al, 1990a) and can be modeled as Gaussians with an average standard deviation of 66° (Blair and Sharp, 1995). In rodents, HD cells have been found in postsubiculum (Taube et al, 1990a,b;Sharp, 1996), in the anterior dorsal thalamic nuclei (Blair and Sharp, 1995;Knierim et al, 1995;Taube, 1995;Blair et al, 1997), in the lateral mammillary nuclei (Blair et al, 1998;Stackman and Taube, 1998), as well as the dorsal tegmental nucleus of Gudden (Sharp et al, 2001b), the lateral dorsal nucleus of the thalamus (Mizumori and Williams, 1993), the striatum (Wiener, 1993;Ragozzino et al, 2001), and the retrosplenial cortex (Chen et al, 1994a,b).…”