Research Faculty

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Sachin Deshmukh

Wellcome Trust DBT Intermediate Fellow

Office : Ground floor of PRL at Central Animal Facility
Phone : +91 80 2293 2830
E-Mail : sachin[at]iisc.ac.in

Research Areas

Neural mechanisms of learning and memory


Research Details

One of the central objectives of systems neuroscience is to understand the neural mechanisms of learning and memory, much of which critically depends on the hippocampus. Understanding the normal process of memory formation in the hippocampal region will facilitate our ability to mitigate the profound memory loss caused by damage to the entorhinal cortex and the hippocampus in Alzheimer’s disease, stroke, traumatic brain injury and epilepsy.

Space is the most conspicuous functional correlate of rodent hippocampal neurons. A prominent theory posits that hippocampal “place cells” constitute a spatial framework, and that items and events of experience are organized within this spatial framework to create a “cognitive map”. Cortical inputs to the hippocampus are channelled through the lateral entorhinal cortex (LEC) and the medial entorhinal cortex (MEC) (fig. 1). While MEC encodes path-integration-derived spatial information, we have recently shown that LEC encodes sensory-derived spatial as well as nonspatial information (fig. 2). Such sensory-derived information is critical to the cognitive map, both for anchoring the spatial representation to the real world using landmarks, as well as for storing (and processing) nonspatial information in the context of spatial information.

Our primary research interest is to understand how the hippocampal network creates a coherent representation of events within their spatial context. Unravelling the interplay of sensory-derived spatial and nonspatial information brought in by LEC and the internally generated, path-integration-based spatial representation in MEC is a crucial step in this endeavour.

We hypothesize that gating of sensory information by LEC plays a role in the creation and maintenance of the representation of space in the hippocampal system. Selecting relevant sensory information (instead of being a passive conduit) may be the vital contribution of LEC to cognitive map formation and function. We will test whether LEC gates sensory information for task relevance, and measure the effect of such gating on the activity of MEC and the hippocampus. Answers to these fundamental questions will help decipher how the cognitive map is created and used during memory formation.

In order to answer these questions, we correlate neuronal activity with ongoing behaviour. We record electrical activity of neurons from the entorhinal cortex, the hippocampus and related areas using hyperdrives capable of positioning individual tetrodes in the target regions of the brain.

 

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Fig. 1 Anatomical organization of entorhinal cortex input to the hippocampus.

 

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Fig. 2 Nonspatial (Unit 1) and spatial(Unit 2) representations in LEC in the presence of objects.

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Fig. 3 Hyperdrive and tetrode used for recording neuronal activity.

Publications

Lee H, Wang C, Deshmukh SS, Knierim JJ, (2015), Neuronal population evidence of functional heterogeneity along the CA3 transverse axis: pattern completion versus pattern separation, Neuron, 87(5):, 1093-105

Deshmukh SS, (2014), Spatial and nonspatial representations in the lateral entorhinal cortex, In: Space, Time and Memory in the Hippocampal Formation, Springer, Vienna, 127-152

Knierim JJ, Neurnuebel JP, Deshmukh SS, (2014), Functional correlates of the lateral and medial entorhinal cortex: Objects, path integration, and local-global reference frames, Phil. Trans. Roy. Soc. B. Biol. Sci. 369 20130369, doi:10.1098/rstb.2013.0369

Deshmukh SS#, Knierim, JJ, (2013), Influence of local objects on hippocampal representations: landmark vectors and memory, Hippocampus. 23:253-267*. (# corresponding author; * pictured on the cover of the April 2013 issue of Hippocampus).

Deshmukh SS*#, Johnson JL*, Knierim JJ, (2012), Perirhinal cortex represents nonspatial, but not spatial, information in rats foraging in the presence of objects: Comparison with lateral entorhinal cortex, Hippocampus. 22:2045-2058. (* equal first-author, # corresponding author)

Deshmukh SS, Knierim JJ, (2011), Representation of non-spatial and spatial information in the lateral entorhinal cortex, Front. Behav. Neurosci. , 5:69

Deshmukh SS, Yoganarasimha D, Voicu H, Knierim JJ, (2010), Theta modulation in the medial and the lateral entorhinal cortices, J. Neurophysiol, 104:994-1006