There are various ways to study neuronal processing of information about temporal frequency content of visual stimuli. The two most fundamental methods are 1) direct measurement of response amplitude, e.g. an amplitude of averaged visual evoked potential, and 2) assessment of response magnitude after transformation of electrophysiological signal from time to frequency domain. In our study we found it impossible to use the same paradigm to analyze the whole spectrum of temporal frequencies in local field potentials recorded during visual electrophysiology experiments performed on anesthetized rats. Visual responses were recorded from all layers of primary visual cortex in response to flashing light with temporal frequency in the range of 0.5 - 15 Hz. We found that for frequencies lower than 2 Hz it is difficult to draw conclusions based on power spectrum alone, while for high frequencies (> 2 Hz) the evoked potential in time domain could not be observed. We discuss possible physiological reasons of these difficulties and the advantages of the Welch method instead of the periodogram to analyze signals in the frequency domain.
The process of learning induces plastic changes in neuronal network of the brain. Our earlier studies on mice showed
that classical conditioning in which monocular visual stimulation was paired with an electric shock to the tail enhanced
GABA immunoreactivity within layer 4 of the monocular part of the primary visual cortex (V1), contralaterally to the
stimulated eye. In the present experiment we investigated whether the same classical conditioning paradigm induces
changes of neuronal excitability in this cortical area. Two experimental groups were used: mice that underwent 7-day
visual classical conditioning and controls. Patch-clamp whole-cell recordings were performed from ex vivo slices of
mouse V1. The slices were perfused with the modified artificial cerebrospinal fluid, the composition of which better
mimics the brain interstitial fluid in situ and induces spontaneous activity. The neuronal excitability was characterized by
measuring the frequency of spontaneous action potentials. We found that layer 4 star pyramidal cells located in the
monocular representation of the “trained” eye in V1 had lower frequency of spontaneous activity in comparison with
neurons from the same cortical region of control animals. Weaker spontaneous firing indicates decreased general
excitability of star pyramidal neurons within layer 4 of the monocular representation of the "trained" eye in V1. Such
effect could result from enhanced inhibitory processes accompanying learning in this cortical area.
Correlation methods were used to characterize the activity of single neurons and network connections in three
subcortical structures of the cat visual system. Autocorrelation analysis performed on spike trains of single cells recorded
from the lateral geniculate and perigeniculate nuclei showed the presence of bursts of high-frequency oscillations
ranging from 100 to 550 Hz in their spontaneous activity. Autocorrelation performed on spike trains of single cells
recorded from the superior colliculus also revealed oscillations, but in the frequency range of 10 - 90 Hz, both in the
spontaneous and visually evoked neuronal activity. The presence of oscillations was confirmed with spectral analysis
and a shift predictor was used to distinguish between stimulus-locked and stimulus-independent oscillations in visually
evoked activities. Additionally, a crosscorrelation analysis performed on two spike trains recorded from the same
electrode or pairs of electrodes in the superior colliculus, revealed a common input from an external source and the
presence of inhibitory interactions in the neuronal network.
To monitor neuronal circuits involved in emotional modulation of sensory processing we proposed a plan to establish novel research techniques combining recent biological, technical and analytical discoveries. The project was granted by National Science Center and we started to build a new experimental model for studying the selected circuits of genetically marked and behaviorally activated neurons. To achieve this goal we will combine the pioneering, interdisciplinary expertise of four Polish institutions: (i) the Nencki Institute of Experimental Biology (Polish Academy of Sciences) will deliver the expertise on genetically modified mice and rats, mapping of the neuronal circuits activated by behavior, monitoring complex behaviors measured in the IntelliCage system, electrophysiological brain activity recordings by multielectrodes in behaving animals, analysis and modeling of behavioral and electrophysiological data; (ii) the AGH University of Science and Technology (Faculty of Physics and Applied Computer Sciences) will use its experience in high-throughput electronics to build multichannel systems for recording the brain activity of behaving animals; (iii) the University of Warsaw (Faculty of Physics) and (iv) the Center for Theoretical Physics (Polish Academy of Sciences) will construct optoelectronic device for remote control of opto-animals produced in the Nencki Institute based on the unique experience in laser sources, studies of light propagation and its interaction with condensed media, wireless medical robotic systems, fast readout opto-electronics with control software and micromechanics.