We are interested in how neurons and their contextual networks accomplish functional computations.
More precisely, we study specific properties in a functional framework, mostly in the visual system.
This study combines several approaches: characterization of intrinsic and synaptic electrophysiological
properties, retrograde tracing in order to investigate how intrinsic properties and circuitry connectivity
combine to give functional characteristics, data analysis and hypothesis testing in a theoretical framework
that is designed specifically to guide the experimental protocols.
My main project focuses on the role of shunting inhibition in the cortical visual processing. More precisely, I am interested in understanding how excitatory and inhibitory inputs interact as part of
visual information processing. We know from the teamís previous work that shunting inhibition evoked with visual input can increase the input conductance of a neuron by a factor of 3 or more. This dramatic increase would be expected to have a large effect on the non-linear integration
of the synaptic inputs, and thus the properties of the cellís receptive field. In order to quantitatively study the influence of shunting inhibition, we have addressed its effect on the neuronís input-output
transfer function. We apply artificial shunting inhibition to neurons to assess how it affects both the f/I curve and the more physiologically relevant f/G curve. These protocols are made with whole-cell patch clamp recordings in visual and somatosensory cortex in vivo, under both
current clamp mode and conductance clamp mode using the dynamic clamp method. Interestingly, we have found that shunting inhibition affects
the input-output transfer function in a different manner than has been previously demonstrated in theoretical and experimental studies (Graham and Schramm, in preparation).
The in vivo approach is motivated by the importance to be as close as possible to the
natural state of neurons, as well as our interest in measuring the impact of shunting on visual responses. However, obtaining high quality, stable recordings with the in vivo blind patch protocol is quite difficult. Thus, as part of my research, and in order to improve the technique, we have developed a new method for better whole cell access, called the ďTouch and ZapĒ protocol (Schramm and Graham, in preparation).