Archive | December 2015

A Combined Clock and Compass

In the case of species evidencing magnetoreception, there is the possibility that cryptochrome (with its connection to both a navigation strategy, and circadian rhythms) may be supporting in an integrated sense of time and place through a system that combined together a clock and compass. Evidence of such a system has been indicated in various species and this is explored further in this posting.  

Vertebrates have multiple compass systems (sun, star, polarized light and magnetic compasses. Factors that determine which of these compass systems is used at any given time include weather conditions, time of day, and past experience.  Each of these compass systems requires different sensory detection/processing mechanisms, e.g., a time compensation mechanism for the sun compass and specialized sensory receptors capable of detecting the plane of polarized light and alignment of the geomagnetic field for the polarized light and magnetic compasses . Each compass system also incorporates to varying degrees both innate and learned components . To avoid systematic errors in the direction of orientation when switching between compasses, each of these systems must be calibrated with respect to a common reference system. In birds, where the integration of compass information is best understood, the primary compass calibration reference appears to be derived from celestial cues, probably polarized patterns present at sunset and, possibly, also sunrise. Accurate navigation only requires that the map and compass are in register with one another, i.e., that the animal navigator is able to associate a geographic position specified by the map with a compass bearing that will enable it to return to the origin of a displacement or to some other predetermined destination.  J B Philips  2006. 

Beyond a combined clock and compass, it may be interesting to consider that memories are not only of places, but of places linked to time.  An integrated navigation system will also need to draw on previous (or predicted) experience.  Therefore focusing on place based memory (as much of the research on place and grid cells has done), without integrating it with time, is likely to provide a limited understanding.   A combined clock and compass system might support a memory that can integrate space-time information. 

“Time is the only physical variable that is ‘inherited’ by the brain from the external world…Thus, memories must be ‘made of time,’ or, more precisely, of temporal relationships between external stimuli…In effect, the entire biological utility of memory relies on the existence of many dimensions of homeostasis, some shorter-term and some longer-term. The many timescales of memory represent many timescales of past experience and must be simultaneously available to the organism to be useful.”   N V Kukushkin 2017.  There are a number of timings/periodic oscillations taking place in the biology, but circadian rhythms  play a  key role in coordinating these across the piece – ensuring that they take place in sequence and support optimum efficiency in the organism.   Read More…