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Information processing in the cerebellum granular layer and changes in plasticity revealing single neuron effects in neural ensembles

Shyam Diwakar1*
  • 1 Amrita University, School of Biotechnology, India

In the current work, an estimate of information flow in terms of spikes in the cerebellum granular layer is discussed. Information transmission at the Mossy Fiber (MF) - Granule cell (GrC) synaptic relay is crucial to understand mechanisms of signal coding in the cerebellum [Albus,1971] [Marr, 1969]. To quantify the information transfer of a whole neuron, we used a computational model of a cerebellar granule cell [Diwakar, 2009], where the excitatory input space could be explored extensively. MFs convey afferent signals to GrCs following sensory stimulation. Plasticity was simulated in the granule cell model by changing the intrinsic excitability and release probability of the cells. Information coding in neurons or brain cells occur as excitatory post-synaptic potentials (EPSPs) and as spikes. The role of both EPSPs and spikes as information content relating the neuron’s response to given input stimuli was explored. LTP favored generation of spikes whereas LTD favored EPSPs as expected, although the percentage of spikes was higher at low release probabilities than the percentage of EPSPs at higher release probabilities. The role of selective inhibition by Golgi cells for coincidence detection is presented.
The cerebellum input stage has been known to perform combinatorial operations on input signals. A detailed network model [Medini, 2010] was developed to study information transmission and signal recoding in the cerebellar granular layer and to test observations like center-surround organization and time-window hypothesis. It was noted that simple neuron models may be used to abstract timing phenomenon in large networks, however detailed models were needed to study changes in synaptic plasticity. Plasticity and its effect in generation and modulation of spikes in the granular layer network have been analyzed. Our results also indicated that spatio-temporal information transfer through the granular network is controlled by synaptic inhibition. Spike amplitude and number of spikes were modulated by LTP and LTD. The granular network operates a robust population code for a wide range of intervals, modulated by the Golgi cell inhibition and was regulated by the post-synaptic excitability.
Understanding population activities of underlying neurons reveal emergent behaviour as patterns of information flow in neural circuits. Local field potentials (LFPs) arise from complex interactions of spatial distribution of current sources, time dynamics, and spatial distribution of dipoles apart underlying conductive properties of the extracellular medium. Hence we reconstructed LFP to test and parameterize the molecular mechanisms of cellular function with network properties. The sensitivity of LFP to local excitatory and inhibitory connections was tested using two novel but simpler approaches [Parasuram, 2010]. Both modelling approaches generated LFP in vitro [Mapelli, 2007] and in vivo [Roggeri, 2008] waveforms as reported in experiments. A third and newer technique called ReConv was designed. ReConv uses repetitive convolutions of jittered post-synaptic potentials to generate LFP as seen in granular layer. Changes to single cell properties during LTP and LTD were reflected in the LFP wave suggesting the sparse recoding function of granule neurons as spatial pattern generators.

Acknowledgements

This work derives direction and ideas from the Chancellor of Amrita University, Sri Mata Amritanandamayi Devi. Author thanks Harilal Parasuram, Chaitanya Medini, Priyanka James, Nimshitha Abdulmanaph, Manjusha Nair, Adam Wayland, Nidheesh Melethadathil for their contribution. This work is supported partially by the Sakshat project of National Mission on Education through ICT, Department of Higher Education, Ministry of Human Resource Department, Government of India.

References

• S. Diwakar, J. Magistretti, M. Goldfarb, G. Naldi, E. D' Angelo, Axonal Na+ channels ensure fast spike activation and back-propagation in cerebellar granule cells. J Neurophysio., 101 (2009).
• L. Roggeri, B. Rivieccio, P. Rossi and E. D' Angelo Tactile stimulation evokes long-term synaptic plasticity in the granular layer of cerebellum. The Journal of Neuroscience, 28 (2008) 25.
• J. Mapelli, E. D' Angelo, The Spatial Organization of Long-term synaptic Plasticity at the Input Stage of cerebellum. The Journal of Neuroscience, 27 (2007).
• J. S. Albus, A theory of cerebellar function. Math Biosci., 10 (1971).
• H. Parasuram, N. Abdulmanaph, B. Nair, S. Diwakar. Modeling granular layer local field potential using single neuron and network based approaches to predict LTP/LTD in extracellular recordings. Proceedings of Neurocomp (Lyon, France), 2010.
• C. Medini, S. Subramaniyam, B. Nair, S. Diwakar. Modeling cerebellar granular layer excitability and combinatorial computation with spikes. Proceedings of IEEE BIC-TA 2010, Sept 8-10, (2010).
• D. A. Marr. A theory of cerebellar cortex. J Physiol (Lond). 202 (1969) 437– 470.

Keywords: action potential, Cerebellar granular layer, computational neuroscience, EPSP, granule neuron, Learning and plasticity, local field potential, network

Conference: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011, Freiburg, Germany, 4 Oct - 6 Oct, 2011.

Presentation Type: Abstract

Topic: learning and plasticity (please use "learning and plasticity" as keyword)

Citation: Diwakar S (2011). Information processing in the cerebellum granular layer and changes in plasticity revealing single neuron effects in neural ensembles. Front. Comput. Neurosci. Conference Abstract: BC11 : Computational Neuroscience & Neurotechnology Bernstein Conference & Neurex Annual Meeting 2011. doi: 10.3389/conf.fncom.2011.53.00230

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Received: 20 Apr 2011; Published Online: 04 Oct 2011.

* Correspondence: Dr. Shyam Diwakar, Amrita University, School of Biotechnology, Kollam, Kerala, 690525, India, shyam@amrita.edu