Application of Parallel Factor Analysis (PARAFAC) to electrophysiological data.

The identification of important features in multi-electrode recordings requires the decomposition of data in order to disclose relevant features and to offer a clear graphical representation. This can be a demanding task. Parallel Factor Analysis (PARAFAC; Hitchcock, 1927; Carrol and Chang, 1970; Harshman, 1970) is a method to decompose multi-dimensional arrays in order to focus on the features of interest, and provides a distinct illustration of the results. We applied PARAFAC to analyse spatio-temporal patterns in the functional connectivity between neurons, as revealed in their spike trains recorded in cat primary visual cortex (area 18). During these recordings we reversibly deactivated feedback connections from higher visual areas in the pMS (posterior middle suprasylvian) cortex in order to study the impact of these top-down signals. Cross correlation was computed for every possible pair of the 16 electrodes in the electrode array. PARAFAC was then used to reveal the effects of time, stimulus, and deactivation condition on the correlation patterns. Our results show that PARAFAC is able to reliably extract changes in correlation strength for different experimental conditions and display the relevant features. Thus, PARAFAC proves to be well-suited for the use in the context of electrophysiological (action potential) recordings.

Pharmacological properties of motion vision in goldfish measured with the optomotor response.

In goldfish, the retinal pathways involved in motion coding have been demonstrated to have an L-cone dominated action spectrum (S. Schaerer, C. Neumeyer, Motion detection in goldfish investigated with the optomotor response is "color blind", Vision Res. 36 (1996) 4025-4034). The neurotransmitters involved in retinal motion coding mechanisms, and the relevance of these retinal motion coding mechanisms for motion perception, are little investigated in fish. In this study, the optomotor response was used to investigate the effect of antagonists on different receptor types for acetylcholine (ACh), GABA, for the dopamine D2-receptor (D2-R) - which is known to modulate the action spectrum in motion coding (C. Mora-Ferrer, K. Behrend, Dopaminergic modulation of photopic temporal transfer properties in goldfish retina investigated with the ERG, Vision Res. 44 (2004) 2067-2081) - and of an agonist for against the mGluR6-receptor (mGluR6) on goldfish motion vision in the photopic range. Blockade of nicotinic ACh-R, GABAa-R and both GABAa- and GABAc-R eliminated the optomotor response completely. Neither a muscarinic ACH-R antagonist, a D2-R antagonist or a mGluR6-agonist affected goldfish motion vision. The pharmacological profile of the goldfish optomotor response resembles the pharmacological profile of direction-selective ganglion cells (DS-GC) described for vertebrate retinas in electrophysiological experiments, e.g. (S. Weng, W. Sun, S. He, Identification of ON-OFF direction-selective ganglion cells in the mouse retina, J. Physiol. 562 (2005) 915-923). This indicates that cells with direction-selective receptive field properties exist in the goldfish retina. It is proposed that these cells provide the input for the full field motion perception in goldfish.

Hemodynamic signals correlate tightly with synchronized gamma oscillations.

Functional imaging methods monitor neural activity by measuring hemodynamic signals. These are more closely related to local field potentials (LFPs) than to action potentials. We simultaneously recorded electrical and hemodynamic responses in the cat visual cortex. Increasing stimulus strength enhanced spiking activity, high-frequency LFP oscillations, and hemodynamic responses. With constant stimulus intensity, the hemodynamic response fluctuated; these fluctuations were only loosely related to action potential frequency but tightly correlated to the power of LFP oscillations in the gamma range. These oscillations increase with the synchrony of synaptic events, which suggests a close correlation between hemodynamic responses and neuronal synchronization.