A Mesoscopic Model of VSD Dynamics Observed in Visual Cortex Induced by Flashed and Moving Stimuli
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1
Bernstein Group for Computational Neuroscience, Germany
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2
Ruhr-Universität Bochum, Institut für Neuroinformatik, Germany
Understanding the functioning of the primary visual cortex requires characterization of the dynamics that underlie visual perception and of how the cortical architecture gives rise to these dynamics. Recent advances in real-time voltage-sensitive dye (VSD) imaging permit the cortical activity of neuronal populations to be recorded with high spatial and temporal resolution. This wealth of data can be related to cortical function, dynamics and architecture by computational modeling. To describe brain dynamics at the population level (as measured by VSD imaging), a mesoscopic model is an appropriate choice.
We present a two-layered neural field model that captures essential characteristics of activity recorded by VSD imaging across several square millimeters of early visual cortex in response to flashed and moving stimuli [1]. Stimulation included the well-known line-motion paradigm [2] (in which apparent motion is inducible by a square briefly flashed before a bar), a single flashed square, a single flashed bar, and squares moving with different speeds.
The neural field model describes an inhibitory and an excitatory layer of neurons as a coupled system of non-linear integro-differential equations [3,4]. The model subsumes pre-cortical and intracortical processing. It has relatively few parameters, all of which can be interpreted functionally. We have extended our simulation and analysis of cortical activity dynamics from one spacial dimension - along the (apparent) movement direction - to the two dimensional cortical sheet. In order to identify the parameters of the dynamical system, we combine linear and derivative-free non-linear optimization techniques [5]. Under the assumption that the aggregated activity of both layers is reflected by VSD imaging, our model quantitatively accounts for the observed spatio-temporal activity patterns (e.g., see supplementary Fig. 1).
Our results indicate that feedback from higher brain areas is not required to produce motion patterns in the case of the illusory line-motion paradigm. Inverting the model suggests that a considerable fraction of the VSD signal may be due to inhibitory activity, supporting the notion that intra-layer cortical interactions between inhibitory and excitatory populations play a major role in shaping dynamic stimulus representations in the early visual cortex.
References
1. Jancke D, Chavane F, Na'aman S, Grinvald A (2004) Imaging cortical correlates of illusion in early visual cortex. Nature 428: 423-426.
2. Hikosaka O, Miyauchi S, Shimojo S (1993) Focal visual attention produces illusory temporal order and motion sensation. Vision Research 33: 1219-1240.
3. Amari SI (1977) Dynamics of pattern formation in lateral-inhibition type neural fields. Biological Cybernetics 27: 77-87.
4. Wilson R, Cowan D (1972) Excitatory and inhibitory interactions in localized populations of model neurons. Biophysical Journal 12: 1-24.
5. Igel C, Erlhagen W, Jancke D (2001) Optimization of Neural Field Models. Neurocomputing 36(1-4): 225-233.
Conference:
Bernstein Conference on Computational Neuroscience, Frankfurt am Main, Germany, 30 Sep - 2 Oct, 2009.
Presentation Type:
Oral Presentation
Topic:
Dynamical systems and recurrent networks
Citation:
Markounikau
V,
Igel
C and
Jancke
D
(2009). A Mesoscopic Model of VSD Dynamics Observed in Visual Cortex Induced by Flashed and Moving Stimuli.
Front. Comput. Neurosci.
Conference Abstract:
Bernstein Conference on Computational Neuroscience.
doi: 10.3389/conf.neuro.10.2009.14.064
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Received:
26 Aug 2009;
Published Online:
26 Aug 2009.
*
Correspondence:
Valentin Markounikau, Bernstein Group for Computational Neuroscience, Bochum, Germany, valentin.markounikau@neuroinformatik.rub.de