High-Resolution Intracellular Methods for Conductance Injection and Measurement in Cerebral Cortical Neurons

Full project (pdf)

The activated cerebral cortex displays "high-conductance states" characterized intracellularly by intense subthreshold fluctuations, which are due to the high-level of activity in the local surrounding network. Present intracellular methods to characterize this activity are limited in resolution due to the bias introduced by recording electrodes. We address these limitations by proposing a new recording paradigm based on a computer-controlled feedback with the cell. Developing and implementing this paradigm requires a tight association between mathematics, computer science, computational neuroscience and intracellular electrophysiology (in vivo and in vitro). We aim at both the conception of novel methodologies, their testing in real neurons (essentially in vitro), as well as applying these methods to intracellular recordings in primary visual cortex in vivo.

This project (coordinated by A. Destexhe) combines different expertises, such as mathematics, computer science, computational neuroscience and intracellular electrophysiology (in vitro and in vivo), to yield accurate and reliable methods to properly characterize high-conductance states in neurons. We plan to address several of the caveats of present recording techniques, namely 1) the impossibility to perform reliable high-resolution dynamic-clamp with sharp electrodes, which is the intracellular technique mostly used in vivo; 2) the unreliability and low time resolution of single-electrode voltage-clamp recordings in vivo; 3) the impossibility of extracting single-trial conductances from Vm activity in vivo. We propose to address these caveats with the following goals:

1. Obtain high-resolution recordings applicable to any type of electrode (sharp and patch), any type of protocol (current-clamp, voltage-clamp, dynamic-clamp) and different preparations (in vivo, in vitro, dendritic patch recordings).

2. Obtain methods to reliably extract single-trial conductances from Vm activity, as well as to "probe" the intrinsic conductances in cortical neurons. These methods will be applied to intracellular recordings during visual responses in cat V1 in vivo.

3. Obtain methods to extract correlations from Vm activity and apply these methods to intracellular recordings in vivo to measure changes in correlation in afferent activity.

4. Obtain methods to estimate spike-triggered averages from Vm activity and obtain estimates of the optimal patterns of conductances that trigger spikes in vivo. These results will be integrated into computational models to test mechanisms for selectivity.

These methods are based on a real-time feedback between a computer and the recorded neuron. This real-time feedback will be used not only to improve existing techniques, but also to extract essential information to better understand spike selectivity of cortical neurons in vivo.

The expected contributions of this project are (a) to provide technical advances in the precision and resolution of several currently used recording techniques, such as dynamic-clamp and voltage-clamp, which are currently limited. We aim at obtaining high resolution (>= 20 KHz) reliable measurement or conductance injection. This advance should be of benefit for in vivo and in vitro electrophysiology. (2) It will enable us to perform precise conductance measurements in high-conductance states in vivo and in vitro and better understand this type of network activity. (3) It will enable us to better understand the spike selectivity of cortical neurons, by directly measuring single-trial conductances underlying visual responses, as well as the conductance time courses linked to the genesis of spikes. The mechanisms of spike selectivity in cortical neurons are still a subject of intense debate, and we expect to provide here crucial measurements of single-trial conductance patterns.

The project involves an interdisciplinary team of researchers from ODYSSEE (INRIA/ENS) and UNIC (CNRS).