Visualization of Cortical Dynamics

Grinvald A.
Department of Neurobiology
Weizmann Inst. of Science
Rehovot, 76100, Israel.

Abstract

Recent progress in studies of cortical dynamics utilizing real time optical imaging based on voltage sensitive dyes will be reviewed including the combination of, single and multi- unit recordings, LFP, intracellular recordings and microstimulation. To image the flow of neuronal activity from one cortical site to the next, in real time, we have used optical imaging based on newly designed voltage sensitive dyes and a Fuji 128 x 128 fast camera which we modified. A factor of 20-40 fold improvement in the signal to noise ratio was obtained with the new dye during in vivo imaging experiments. This improvements has facilitates the exploration of cortical dynamics without signal averaging in the millisecond time domain. The following findings will be covered: We confirmed that the voltage sensitive dye signal indeed reflects membrane potential changes in populations of neurons by showing that the time course of intracellular recordings from single neurons was highly correlated in many cases with the optical signal from a small patch of cortex recorded nearby (but as expected, only under deep anesthesia). We found that the degree of cortical synchronization as reflected from the relationship between the membrane potential changes in individual neurons and the population activity was large. We showed that the dynamics of coherent activity in neuronal assemblies can be visualized and found that the instantaneous cortical activity is the sum of a reproducible stimulus response component and the on-going network dynamics. In addition we showed that the firing of single cortical neurons is not a random process but occurs when the on-going pattern of million of neurons is similar to the functional architecture map which correspond to the tuning properties of that neuron. Furthermore, we showed that spontaneously occurring cortical states, in the absence of any visual input often correspond to the orientation domain and are dynamically switching. We have also investigated the dynamics of shape processing by exploring the development of orientation selectivity in the millisecond time domain. The cortical correlation of a visual illusion were revealed in another study. Chronic optical imaging, combined with electrical recordings and microstimulation, over a long period of times of more than a year, was successfully applied also the study of similar questions in the behaving macaque monkey.

For additional information see:

• Shoham et al., (1999). Imaging cortical architecture and dynamics at high spatial and temporal resolution with new voltage-sensitive dyes. Neuron, 24, 1-12;
• Tsodyks et al., (1999). The spontaneous activity of single cortical neuron depends the underlying global functional architecture. Science, 286, 1943-1946;
• Grinvald et al., (1999). In-vivo Optical Imaging of cortical Architecture and Dynamics. A. in Modern Techniques in Neuroscience Research. Windhorst and Johansson (Eds.) Springer Verlag, pp 893-969;
• Sharon and Grinvald (2002) Dynamics and constancy in cortical spatiotemporal patterns of orientation processing. Science, 295, 512-515;
• Seidemann et al., (2002) Dynamics of depolarization and hyperpolarization in the frontal cortex and saccade goal. Science, 295(5556):862-865.

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