Receptive field analysis in cat primary visual cortex
AuthorSun, Shi Hai
AffiliationOptometry and Vision Sciences
Document TypePhD thesis
Access StatusOpen Access
© 2019 Shi Hai Sun
Characterising receptive fields (RFs) in the primary visual cortex (V1) is central to understanding how neurons and neural circuits process visual information. The goal of this thesis is to systemically compare the two most robust RF characterisation techniques available. The best performing technique will then be used to correlate spatial RFs to two fundamental neuronal properties in V1: cell classification (using extracellular spike identification); and contrast adaptation. I recorded (extracellularly) and estimated the RFs of anaesthetised cat V1 neurons in response to white-Gaussian noise (WGN) using 32-channel array probes. Single units were characterised using the generalised quadratic model (GQM), which is based on prior knowledge and assumptions about cortical processing, and the nonlinear input model (NIM), which is a more physiologically based parametric modelling framework. Qualitatively, the variability between the two models increased as the number of required filters increased. I also compared the performance of the two models quantitatively and found that it is better to use the more parametric framework of the NIM for RF characterisation than the GQM, though those advantages depend somewhat on the availability of spiking data. In the next part of my thesis, I extracted the extracellular spikes of V1 neurons and correlated their shapes to their spatial RFs extracted using the NIM. Extracellular spike waveforms from recordings in V1 have traditionally consisted of negative first phases. I identified these spike types in my data, but I show that there are also distinct classes of spikes with positive first phases. The RFs and spiking characteristics of these different spike waveform types were examined, and I found that the negative spiking units showed characteristics typical of cortical cells (i.e. simple and complex cell types) and the positive first phase spiking units showed characteristics typical of thalamic cells, which provide the input to cortex. To further investigate this theory, I recorded from V1 before and after cortical silencing, and found that only positive first phase spikes remained. This provides strong evidence in support of the theory that the positive first phase spikes are derived from the thalamic input fibres to the cortex. For the final part of the project I recovered the RFs (using NIM) of neurons during adaptation to drifting gratings (i.e. contrast adaptation). There were no consistent changes in the spatial RFs following contrast adaptation for either simple or complex cells. I also observed that the responses to WGN images of adapted units were significantly slower than the control units (i.e. response latency was increased). However, there were several limitations that arose from this project, which are discussed in detail. The results of my work have demonstrated three aspects of V1 processing: (1) the NIM is better than the GQM for RF characterisation; (2) some extracellular positive first phase spiking units may correspond to recordings from thalamic axons projecting to V1; and (3) contrast adaptation has no effect on the spatial RFs, but it does have an effect on the temporal RFs of cortical V1 neurons.
KeywordsVisual Cortex; Cat; Receptive field; Extracellular spike waveform; Contrast adaptation
- Click on "Export Reference in RIS Format" and choose "open with... Endnote".
- Click on "Export Reference in RIS Format". Login to Refworks, go to References => Import References