The SINTN seminar series proudly presents

Michael Hasselmo

Oscillations, grid cells and memory

Michael Hasselmo D.Phil.
Professor and Associate Director
Center for Memory and Brain, Department of Psychology and Program in Neuroscience, Boston University

Website: Hasselmo lab Web Site

Abstract:

Recent slice physiology, unit recording and computational modeling demonstrate the potential role of oscillatory dynamics and persistent firing in entorhinal cortex neurons for memory function. Whole cell patch data from my laboratory shows that neurons in dorsal entorhinal cortex have higher intrinsic resonance and membrane potential oscillation frequencies than ventral neurons (Giocomo et al., 2007; Giocomo and Hasselmo, 2008). This data scales with the spacing between firing fields of entorhinal grid cells, which fire in a hexagonal array of locations as a rat explores the environment. The scaling of frequency to grid cell spacing provides experimental support for a model of grid cell firing by Burgess, Barry and O’Keefe in which interference between oscillations generates realistic grid cell spiking activity in a virtual rat. Strengths and weaknesses of this model will be discussed in comparison to alternate models. Mechanisms for stable persistent firing of entorhinal neurons (Yoshida et al., 2008) may also underlie grid cell firing patterns (Hasselmo, 2008b) and could provide mechanisms for active maintenance for memory encoding (Hasselmo and Stern, 2006). Grid cell models incorporated in a network model of episodic memory function allow accurate encoding and retrieval of spatial trajectories (Hasselmo, 2008a), using interactions with place cells and head direction cells with persistent spiking (Yoshida and Hasselmo, 2009). These models also replicate data on the context-dependent firing of neurons in a spatial alternation task (Lee et al., 2006) and a range of other behavioural tasks. The model can replicate temporally structured replay of place cell activity during REM sleep (Hasselmo, 2008a). The same mechanisms used to model temporally structured replay could mediate the episodic encoding and retrieval of trajectories to guide behaviour in memory tasks.

Giocomo, L.M., Hasselmo, M.E. (2008) Time constant of I(h) differs along dorsal to ventral axis of medial entorhinal cortex. J. Neurosci., 28:9414-25

Giocomo LM, Zilli EA, Fransen E, Hasselmo ME. (2007) Temporal frequency of subthreshold oscillations scales with entorhinal grid cell field spacing. Science, 315:1719-22.

Hasselmo, M.E. (2008a) Temporally structured replay of neural activity in a model of entorhinal cortex, hippocampus and postsubiculum. Eur. J. Neurosci. 28:1301-1315

Hasselmo M.E. (2008b) Grid cell mechanisms and function: Contributions of entorhinal persistent spiking and phase resetting. Hippocampus. 2008;18(12):1213-29.

Hasselmo, M.E., Stern, C.E. (2006) Mechanisms underlying working memory for novel information. Trends in Cognitive Sciences, 10(11):487-93.

Lee I, Griffin AL, Zilli EA, Eichenbaum H, Hasselmo ME (2006) Gradual translocation of spatial correlates of neuronal firing in the hippocampus toward prospective reward locations. Neuron, 51: 639-50.

Yoshida, M., Fransen, E., Hasselmo, M.E. (2008) mGluR-dependent persistent firing in entorhinal cortex layer III neurons. Eur. J. Neurosci. 28(6):1116-26.

Yoshida M., Hasselmo M.E. (2009) Persistent firing supported by an intrinsic cellular mechanism in a component of the head direction system. J Neurosci. 29(15):4945-52.

Recent Papers:

[1] Giocomo LM, Zilli EA, Fransen E, Hasselmo ME. (2007) Temporal frequency of subthreshold oscillations scales with entorhinal grid cell field spacing. Science, 315:1719-22.

[2] Hasselmo, M.E., Stern, C.E. (2006) Mechanisms underlying working memory for novel information. Trends in Cognitive Sciences, 10(11):487-93.

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