According to the vertebrate literature, I got the impression that head-direction cells are always anchored to an allocentric reference frame. This can easily be tested with freely moving animals. But what is about tethered animals that can freely rotate around their body axis but can`t change their actual position. Are neurons encoding the animals heading automatically defined as allocentric ones? Or how could you test with a tethered approach, if the neurons encode heading in a allocentric reference frame or in an egocentric one?
Very good question. Short answer: "No." Correct me if I'm wrong, but this notion about RF only applies at the cognitive or inferential level (so "Yes" to your answer if your primarily concern deals with spatial cognition mechanisms), at the neuronal/cellular level, I don't think there's any convincing evidence out there showing that neuronal firings converge strictly with the use of one type of RF. This is because humans are perfectly capable of using both types of RFs - ego and allo, and this preference at the cognitive level can influence or be influenced by social and environmental factors at the macro level and neuronal and/or molecular activity at the micro level. If you read the original works documenting the discovery of the place cells (O'Keefe et al.), you shall see that there are certain types of place cells that fire only when the rat were placed in certain spot AND in a certain orientation/direction in its enclosure. So in a way, they possess the same properties as the head direction cells, but you cannot specify whether the rat was actually using an ego RF or allo RF, since either type of RF could be used for cognitive mapping of a small enclosure. Such observations are mentioned in a past review of mine, in which I discussed place cells, head orientation cells,, and grid cells in relation to wayfinding and path integration: Thesis Neural mechanisms of human path integration: Developments ov...
Doesn‘t heading computation by definition always require an allocentric reference frame in the sense that a reference direction needs to be anchored to the environment. Any reference aligned with the navigator would always be zero (as it moves with the navigator)?
See also Klatzky‘s chapter on definition of the terms (Klatzky, R. L. (1998). Allocentric and egocentric spatial representations: Definitions, distinctions, and interconnections. In Spatial cognition (pp. 1-17). Springer, Berlin, Heidelberg.)
M Jerome Beetz , to substantiate what I said, please refer to recent research like this one (link below) which showed neuronal heading signals in the monkey's parietal cortex (in the VIP) can code for both allocentric and egocentric RFs : https://www.pnas.org/content/115/14/E3305
To support the first statement in Prof. Klaus Gramann 's answer and the article he recommended (must-read, IMO), please refer to a mathematical psychology paper of mine (pp.101-102):
Article Reanalysis of an Allocentric Navigation Strategy Scale based...
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