================================================================================================== B. Poucet, P. P. Lenck-Santini, V. Hok, E. Save, J. P. Banquet, P. Gaussier, and R. U. Uuller (2004) "Spatial navigation and hippocampal place cell firing: The problem of goal encoding." Neurosciences Vol, 15, ppl 89--107. ================================================================================================== [Abstract] The place cell system nevertheless requires other essential elements to be competent, such as a component that specifies the overall goal of the animal and comutes the path required to take the rat from its current location to the goal. [Introduction] Performance in the water maze navigation task, in which the rat is demonstably able to find rapidly a hidden platform using the array of available visual cues, is currently the prototypical illustrative example / 55,63,113 [Fundamental properties of place cells] -------------------------------------------------------------------------------------------------- Self-motion information also may be important in the absence of external cues /58,72,89,100/ [58] McNaughton BL, Barnes CA, Gerrard JL, Gothard K, Jung MW, Knioerim JJ, Kudrimoti H, Qin Y, Skaggs WE, Suster M, Weaver KL. (1996) Deciphering the hippocampal polyglot: the hippocampus as a path integration syustem. J Exp Biol 119, pp. 173-185. [72] O'Keefe J. (1976) Place units in the hippocampus of the freely moving rat Exp. Enurol 51, pp. 78-109. [89] G.J. Qiorl. R.U. Miller, J.L. Kubie (1990) The firing of hippocampal place cells in the dark depends on the rat's recent experience J. Neurosci. 10 pp. 2008-2017. [100] Sharp P.E., H.T. Blair, D. Etkin, D.B. Tzanetos (1995) Influences of vestibular and visual motion information on the spatial firing patterns of hippocampal place cells. J. Neurosci 15 pp. 173-189 [Place cell firing and the coding of distinct environments] -------------------------------------------------------------------------------------------------- Ultimately, however, place cells collectively provide information about both the rat's current envirionment and therat's location within the environment. [4.3] -------------------------------------------------------------------------------------------------- not-yet skip if not enough time ~~~~~~~~~~~~~~~~~~~~~~~ until -------------------------------------------------------------------------------------------------- [5. Neural implementation of place navigation:" the problem of the goal location] the main signal carried by place cells, the rat's moment-to-moment location in its current environment, is not sufficient for the rat to compute paths. At least two other crucial kinds of information are necessary for it to be possible to compute complete paths, namely, a representation of the goal and of the sequence of movements to get from the current loacation to the goal. We now briefly describe two classes of solutions to how the goal and progress tho the goal are represented. [5.1 Hippocampus-only models] Following the discovery of place cells, O'Keefe and Nadel [76] proposed a model system, centered on the hippocampus, whose main role was to implement spatial navigation functions. Since then, several investigatiors have proposed schemes that rely on the fact that place cells and the hippocampal machinery can potentially provide the animal with all information requierd to compute paths through the environment. It is not in the scope of this short review to describe these models full [110] but it is useful to state their basics if only to say how they are lacking. [110] Trullier O. Wiener S. Berthoz A, Meyer J.A. "Biologically based artifical navigation system: review and prospects." Prog Neurobiol 1997 51 483-544 => not available for free => gva In a related model, exploration by the rat allows place cells to be linked by synapses whose strength represent in a general way the distance between their firing fields [69] [69] Muller R.U. M. Stead, J. Pach (1996) "The hippocampus as a cognitive graph." J. Gen Physiol 1996 107 663-694 => done Thus, LTP-modifiable connections between place cells with fields that are close to each other would be strengthened because the cells fire in close temporal contiguity. In contrast, connections between place celss with widely separated fields would be weak because such cells cannot fire together. This encoding of distance is a consequence of connecting place cells by Hebbin-like synapses and could occur in the recurrent pyramidal cell to pyramidal cell connecttions in CA3. ... it permits the animal to find an optimal path from any starting point -------------------------------------------------------------------------------------------------- As the rat runs from its starting position to the goal during learning, place cells along the route fire in sequence so that synapses connecting place cells with adjacent fields are strengthened. When the rat is again at the starting point of such a sequence, the whole series of place cells can be replayed, therby allowing the rat to follow the path from cell to cell so that it eventually gets to the goal. In contrast, connections between place cells with widely separated field would be weak because such cells cannot fire together. This encoding of distnace is a consequence of connectiong place cells by Hebbian-like syanpse and could occur in the recurrent pyramidal cell to pryramidal cell connection in CA3. This model has the advantage that it does not rely on previously taken paths: it permits the animal to find an optimal path from any starting point to any goal location in a familiar environment. -------------------------------------------------------------------------------------------------- [5.2 Distributed models] -------------------------------------------------------------------------------------------------- ... by hypothesis, hippocampally supplied transition information from the entire environment is linked to each other in the prefrontal cortex so that it form continuous path. ... The job of the prefrontal cortex is to build a path from the current location to the goal using the transition information from the hippocampus. Activation of these nodes progressively diffuses through the prefrontal graph of learned transitions leading to the goal allowing identification of the optimal/shortes path to the goal. [5.3 Preliminary evidence for goal cells: A unit recording study of the prefrontal cortex] -------------------------------------------------------------------------------------------------- "In the model proposed by Gaussier et al. [21] spatial planning relies on the activity of a prefrontal network which associates places with their motivational valence and is theregfore able to specify goals. [21] Gaussier p, Revel A, Banquet JP, Babeau V. (2002) "From view cells and place cells to cognitive map learning: processsing stages of the hippocampal system." Biol Cybern 86, pp. 15-28" => done With regard to spatial navigation, the behavioral output of the three-module system is the production of smooth and direct paths oriented towards the goal location [3,21] [3] Banquet JP, Gaussier P, Quoy M, Revel A Burnod Y Cortico-hippocampal maps and navigation strategies in robots and rodents From Animals to Animats 7 MIT Press, 141-150 in my paper ================================================================================================== [path-finding] Such kind of empty environment is not so easy to explore as imagined. In many applicatiopn of path-finding, obstacles sometimes are not obstacle but guides to the goal. So simple search reveals such environment cannot be find (except for) Hereafter our target is ... almost shortest path from (0,0) to (0,n) ... [Consious] ... quate "..." in his "study of concious" since o'qiffe'f paper many ... has been reported ... rat navigation here again our target is ...