Nanostimulation: Manipulation of Single Neuron Activity by Juxtacellular Current Injection

Abstract

In the mammalian brain, many thousands of single-neuron recording studies have been performed but less than 10 single-cell stimulation studies. This paucity of single-cell stimulation data reflects a lack of easily applicable single-cell stimulation techniques. We provide a detailed description of the procedures involved in nanostimulation, a single-cell stimulation method derived from the juxtacellular labeling technique. Nanostimulation is easy to apply and can be directed to a wide variety of identifiable neurons in anesthetized and awake animals. We describe the recording approach and the parameters of the electric configuration underlying nanostimulation. We use glass pipettes with a DC resistance of 4-7 Mohms. Obtaining the juxtacellular configuration requires a close contact between pipette tip and neuron and is associated with a several-fold increase in resistance to values > or = 20 Mohms. The recorded action potential (AP) amplitude grows to > or = 2 mV, and neurons can be activated with currents in the nanoampere range--hence the term nanostimulation. While exact AP timing has not been achieved, AP frequency and AP number can be parametrically controlled. We demonstrate that nanostimulation can also be used to selectively inhibit sensory responses in identifiable neurons. Nanostimulation is biophysically similar to electroporation, and based on this assumption, we argue that nanostimulation operates on membranes in the micrometer area directly below the pipette tip, where membrane pores are induced by high transmembrane voltage. There is strong evidence to suggest that nanostimulation selectively activates single neurons and that the evoked effects are cell-specific. Nanostimulation therefore holds great potential for elucidating how single neurons contribute to behavior.

What single-cell stimulation has told us about neural coding

“…In a similar fashion, manipulation of single step current duration without changing its intensity evoked an increased number of spikes at a constant frequency. To parametrically vary the irregularity of the evoked APs, pseudo-random sequences of short step currents of different durations and frequencies as well as periods of inhibition by negative step current pulses were combined [44]. These trials were compared with a single step current of similar duration, which resulted in a regular firing pattern.…”

Consistent Phosphenes Generated by Electrical Microstimulation of the Visual Thalamus. An Experimental Approach for Thalamic Visual Neuroprostheses

“…Consequently, stimulation with high frequencies should lead to more spatially localized current patterns. Moreover, the development of very advanced probes with a high number of fine tips could be useful to select and stimulate individual thalamo-cortical fibers (Houweling et al, 2010); stimulation of appropriate single neuron projections could also be used to promote activation of inhibitory cortical circuits to limit spatial diffusion of the activity. However, although the architecture of the thalamic nuclei has been well established and the functional properties of their neurons have been extensively examined, the ideal type of stimulation is not “a priori” predictable and stimulation parameters need to be varied in a heuristic, trial-and-error procedure.…”

Inferring synaptic connectivity from spatio-temporal spike patterns

“…To begin with, it is model dependent, and has to be given fixed known parameter values, even though these values need not be the same for every neuron in the network. As well, the method requires injection of external currents to individual neurons with a precision not yet generally achievable in an experimental setting (Houweling et al, 2010), nor will it work with externally undriven or weakly driven systems. While with some modification it can handle bounded amounts of noise and/or uncertainty, it is sensitive to errors with respect to, e.g., spike sorting.…”