Path integration 2905826 219973421 2008-06-17T18:30:09Z Fratrep 4541225 Repairing link to disambiguation page - [[Wikipedia:Disambiguation pages with links|You can help!]] {{see also|path integral}} '''Path integration''' is the name given to the method thought to be used by animals for [[dead reckoning]]. [[Charles Darwin]] and [[J.J. Murphy]] first postulated an inertially-based [[navigation]] system in animals in [[1873]]. Studies beginning in the middle of the 20th century confirmed that animals could return directly to a starting point, such as a nest, in the absence of [[Visual perception|vision]] and having taken a circuitous outwards journey. This shows that they can use cues to track distance and direction in order to estimate their position, and hence how to get home. This process was named ''path integration'' to capture the concept of continuous integration of movement cues over the journey. Manipulation of inertial cues confirmed that at least one of these movement (or ''[[idiothetic]]'') cues is information from the [[vestibular organs]], which detect movement in the three [[dimension]]s. Other cues probably include [[proprioception]] (information from muscles and joints about limb position), motor efference (information from the motor system telling the rest of the brain what movements were commanded and executed), and [[optic flow]] (information from the visual system signaling how fast the visual world is moving past the eyes). Together, these sources of information can tell the animal which direction it is moving, at what speed, and for how long. The question of how the animal's brain integrates this dynamic information, in order to draw conclusions about position and homing information, remains unanswered. Extensive studies in [[arthropods]], most notably in the [[Sahara desert ant|desert ant]] ''Cataglyphis fortis'', reveal the existence of highly effective path integration mechanisms that depend on determination of directional heading (by polarizing cues such as the sun) and distance computations (by, essentially, “counting footsteps”). How these sources of information are integrated is not yet known. In mammals, three important discoveries promise to shed light on this issue. The first, in the early 1970s, is that neurons in the [[Hippocampus|hippocampal formation]], called [[Place cell|place cells]], respond to the position of the animal. The second, in the early 1990s, is that [[neuron]]s in neighboring regions (including anterior [[thalamus]] and post-[[subiculum]]), called [[head direction cells]], respond to the head direction of the animal. This enables a much more fine-grained study of path integration, since it is possible to manipulate movement information and see how place and head direction cells respond (a much simpler procedure than training an animal, which is very slow). The third finding was that neurons in the dorso-medial [[entorhinal cortex]], which feeds information to the place cells in the hippocampus, fire in a metrically regular way across the whole surface of a given environment. The activity patterns of these [[grid cells]] looks very much like a [[hexagonal]]ly organized sheet of [[graph paper]], and suggest a possible metric system that place cells can use to compute distances. Whether place and grid cells actually compute a path integration signal remains to be seen, but computational models exist suggesting this is plausible. Certainly, brain damage to these regions seems to impair the ability of animals to path integrate. == References == * Best PJ, White AM, Minai A (2003) Spatial processing in the brain: the activity of hippocampal place cells. ''Annu Rev Neurosci'' 24: 459-486. * Etienne AS, Jeffery KJ (2004) Path integration in mammals. ''Hippocampus'' 14: 180-192. * McNaughton BL, Battaglia FP, Jensen O, Moser EI, Moser MB (2006) Path integration and the neural basis of the 'cognitive map'. ''Nat Rev Neurosci'' 7: 663-678. * Taube JS (1998) Head direction cells and the neurophysiological basis for a sense of direction. ''Prog Neurobiol'' 55: 225-256. ==See also== * [[Dead reckoning]] [[Category:Orientation]] [[Category:Cognitive neuroscience]]