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Gaze Anticipation Contributes to the Steering of Locomotion
Published in Michael Fetter, Thomas Haslwanter, Hubert Misslisch, Douglas Tweed, Three-Dimensional Kinematics of Eye, Head and Limb Movements, 2020
R. Grasso, S. Glasauer, Y. Takei, A. Berthoz
It is tempting to put this finding in relation with the recent discovery by Blair et al. (1995) of the anticipatory tuning of head direction cells in the antedorsal nucleus of the rat thalamus. These cells seem to be tuned with the future direction of the head suggesting they are related to heading rather than to the current head orientation. Indeed, we found that the head anticipation interval and tonic deviation θ tended to increase with the curvature. This indicates that subjects turned their head more and more depending on how much they intended to curve. This study complements the results obtained by Glasauer in a different locomotor task (Glasauer et al., 1995). Astronauts walking along triangular trajectories systematically turned their head before reaching the corners of a triangular path, by a time interval (250–350 ms) not far from the one we found. The larger values he found can be easily explained by the fact that the curvature required to turn around the corners and their linear speed when they were approaching the corner was greater than that found in our experiment.
John O’Keefe (b. 1939)
Published in Andrew P. Wickens, Key Thinkers in Neuroscience, 2018
The cognitive mapping theory received further support when various cells involved in directional “dead reckoning” types of computation were identified. The first of these were discovered in the early 1980s when O’Keefe, along with Bruce McNaughton and Carol Barnes, who were visiting postdoctoral students to his laboratory, found place cells in the hippocampus whose firing rate was dependent on the animal’s speed of movement. That is, the faster the speed, the more the neuron fired. Moreover, many of these cells also had a movement bias – becoming active when the rat moved in one particular direction. Soon after this, O’Keefe would also go on to find a small number of “pure speed cells” in the hippocampus that fired irrespective of the animal’s location or its direction of movement. In New York, another team of investigators led by Jim Ranck would show cells in the subiculum (an area adjacent to the hippocampus) that specifically signalled the animal’s head direction. Intriguingly, these head direction cells could also become “confused” when the rat was spun around – so that a cell that had an original north-east bias might now be altered to point in an eastward direction. And a third type of cell, called “boundary cells” by O’Keefe, was found during the 1990s in several regions of the hippocampal formation, which only responded to an environmental boundary at a particular distance and direction from the animal.
Cataglyphis meets Drosophila
Published in Journal of Neurogenetics, 2020
First, in the ‘flight simulator’ tethered flies can choose an arbitrary direction relative to a green light spot, which arguably they interpret as the sun (see the honeybee’s ‘spectral image’ of the sky; Rossel & Wehner, 1984), or relative to the e-vector orientation of a beam of polarized light presented overhead, and can maintain this direction over several hours even after flight interruptions (Giraldo et al., 2018; Warren, Weir, & Dickinson, 2018). As the latter behavior shows, the flies must be able to compare their current view of the (artificial) sky with a desired remembered one, and hence exhibit some minimum requirement of sky-compass orientation. By calcium-imaging, the neural activity of head direction cells discovered and analyzed by Seelig and Jayaraman (2015) and Turner-Evans et al. (2017) in the fly’s central complex, Giraldo et al. (2018) found that these ‘wedge cells’ (E-PG neurons) encode the sun’s azimuthal position. If the neurons are silenced, this ability breaks down, and the flies switch to flying positively phototactically toward the artificial sun. In this respect, it is interesting to note that under certain conditions also the navigating Cataglyphis exhibits such phototactic responses. When in particular test situations, it cannot use either the polarization or the spectral gradients in the sky as compass cues, and is left alone with the sun presented within a monochromatic, long-wavelength visual environment, its navigational courses are systematically contaminated by phototactic deviations toward the direction of the sun (Wehner, 1997).