Article Figures & Data
Figures
Additional Files
Supplemental Data
Files in this Data Supplement:
- supplemental material - Supplemental Material
Files in this Data Supplement:
The results presented in Diba and Buzsaki are consistent with a realignment of a single map on a trial by trial basis.
This hypothesis of realignment was first proposed by Samsonovich and McNaughton (1997) in their simulations of Gothard et al (1996). Although the Samsonovich and McNaughton paper does include a proposal for multiple maps (or "charts"), in fact, the realignment can also occur within a single map (Zh...
The results presented in Diba and Buzsaki are consistent with a realignment of a single map on a trial by trial basis.
This hypothesis of realignment was first proposed by Samsonovich and McNaughton (1997) in their simulations of Gothard et al (1996). Although the Samsonovich and McNaughton paper does include a proposal for multiple maps (or "charts"), in fact, the realignment can also occur within a single map (Zhang, 1996). The hippocampal system can be interpreted as an internal attractor network with external inputs from sensory and dead-reckoning systems. The internal attractor dynamics force the system to maintain a coherent representation of a single map even under conditions of mismatch between the sensory and dead-reckoning systems. Learning occurring across the external inputs can reset a misaligned map. See Redish (1999) for a comprehensive review of these issues. The results from Redish et al (2000) show that on these compression-track tasks, the animal has a single map (for a given direction) that realigns on each trial depending on the amount of time the animal has been in the environment, consistent with an energy-barrier dynamic.
In the changed environment in the paper (Diba and Buzsaki 2008), the realignment hypothesis suggests that each trial will consist of three stages: alignment to the left wall coordinate system, realignment to the room coordinate system, and then realignment to the right wall coordinate system. Because the realignment events are fast (<<1 second, Redish et al, 2000; proposed to be on the order of a theta cycle or sharp wave, Samsonovich and McNaughton, 1997; Redish and Touretzky, 1998; Redish 1999), most theta cycles will not entail realignment and place fields will maintain their within-theta relationships. It will only be on the very transient re-alignment events that one would see a breakdown in the theta relationships. Because these realignment events should only occur twice on each lap and should occur at different locations on each trial, they will not be observable from across-trial averages. The compressed place fields observed by Diba and Buzsaki (2008) are due to averaging across many trials, each with a different realignment point. A trial-by-trial or moment-by-moment self-consistency analysis (Redish et al., 2000; Jackson and Redish, 2004) would prove this hypothesis.
References
Diba K, Buzsaki G (2008) Hippocampal network dynamics constrain the time lag between pyramidal cells across modified environments. Journal of Neuroscience 28(50):13448-13456.
Gothard KM, Skaggs WE, McNaughton BL (1996) Dynamics of mismatch correction in the hippocampal ensemble code for space: Interaction between path integration and environmental cues. Journal of Neuroscience 16(24):8027-8040.
Jackson JC, Redish AD (2003) Detecting dynamical changes within a simulated neural ensemble using a measure of representational quality. Network: Computation in Neural Systems 14:629-645.
Redish AD (1999) Beyond the Cognitive Map: From Place Cells to Episodic Memory. Cambridge MA: MIT Press.
Redish AD, Rosenzweig ES, Bohanick JD, McNaughton BL, Barnes CA (2000) Dynamics of hippocampal ensemble realignment: Time vs. space. Journal of Neuroscience 20(24):9289-9309.
Redish AD, Touretzky DS (1998) The role of the hippocampus in solving the Morris water maze. Neural Computation 10(1):73-111.
Samsonovich AV, McNaughton BL (1997) Path integration and cognitive mapping in a continuous attractor neural network model. Journal of Neuroscience 17(15):5900-5920.
Zhang K (1996) Representation of spatial orientation by the intrinsic dynamics of the head-direction cell ensemble: A theory. Journal of Neuroscience 16(6):2112-2126.