Transient changes of electrical activity in the rat barrel cortex during conditioning

Abstract To reveal the dynamics of neurophysiological changes in the rat barrel cortex induced by conditioned stimulation we recorded the local niicroelectroencephalographic (EEG) activity and evoked potentials (EPs) in barrel cortex to stimulation of a single vibrissa before and after pairing it with a mild electric shock applied to the rat's tail. Following the introduction of the reinforcing stimulus, the amplitude of the first negative component of evoked potentials in the cortex on the conditioned side grew in relation to the same component of control potentials, evoked by stimulation of the opposite symmetrical vibrissa. This change was accompanied by a latent decrease in spectral power of the EEG within the alpha and beta frequency bands in both hemispheres. The observed changes in both of these electrical manifestations of enhanced neuronal activity reverted after two (EP) or three (EEG) days of conditioning. These results are discussed in relation to the putative activity of neuromodulatory systems

Retinal Origin of Electrically Evoked Potentials in Response to Transcorneal Alternating Current Stimulation in the Rat

PURPOSE: Little is known about the physiological mechanisms underlying the reported therapeutic effects of transorbital alternating current stimulation (ACS) in vision restoration, or the origin of the recorded electrically evoked potentials (EEPs) during such stimulation. We examined the issue of EEP origin and electrode configuration for transorbital ACS and characterized the physiological responses to CS in different structures of the visual system. METHODS: We recorded visually evoked potentials (VEPs) and EEPs from the rat retina, visual thalamus, tectum, and visual cortex. The VEPs were evoked by light flashes and EEPs were evoked by electric stimuli delivered by two electrodes placed either together on the same eye or on the eyeball and in the neck. Electrically evoked potentials and VEPs were recorded before and after bilateral intraorbital injections of tetrodotoxin that blocked retinal ganglion cell activity. RESULTS: Tetrodotoxin abolished VEPs at all levels in the visual pathway, confirming successful blockage of ganglion cell activity. Tetrodotoxin also abolished EEPs and this effect was independent of the stimulating electrode configurations. CONCLUSIONS: Transorbital electrically evoked responses in the visual pathway, irrespective of reference electrode placement, are initiated by activation of the retina and not by passive conductance and direct activation of neurons in other visual structures. Thus, placement of stimulating electrodes exclusively around the eyeball may be sufficient to achieve therapeutic effects

Cholinergic and Noradrenergic Modulation of Corticothalamic Synaptic Input From Layer 6 to the Posteromedial Thalamic Nucleus in the Rat

Cholinergic and noradrenergic neuromodulation of the synaptic transmission from cortical layer 6 of the primary somatosensory cortex to neurons in the posteromedial thalamic nucleus (PoM) was studied using an in vitro slice preparation from young rats. Cholinergic agonist carbachol substantially decreased the amplitudes of consecutive excitatory postsynaptic potentials (EPSPs) evoked by a 20 Hz five pulse train. The decreased amplitude effect was counteracted by a parallel increase of synaptic frequency-dependent facilitation. We found this modulation to be mediated by muscarinic acetylcholine receptors. In the presence of carbachol the amplitudes of the postsynaptic potentials showed a higher trial-to-trial coefficient of variation (CV), which suggested a presynaptic site of action for the modulation. To substantiate this finding, we measured the failure rate of the excitatory postsynaptic currents in PoM cells evoked by "pseudominimal" stimulation of corticothalamic input. A higher failure-rate in the presence of carbachol indicated decreased probability of transmitter release at the synapse. Activation of the noradrenergic modulatory system that was mimicked by application of norepinephrine did not affect the amplitude of the first EPSP evoked in the five-pulse train, but later EPSPs were diminished. This indicated a decrease of the synaptic frequency-dependent facilitation. Treatment with noradrenergic alpha-2 agonist clonidine, alpha-1 agonist phenylephrine, or beta-receptor agonist isoproterenol showed that the modulation may partly rely on alpha-2 adrenergic receptors. CV analysis did not suggest a presynaptic action of norepinephrine. We conclude that cholinergic and noradrenergic modulation act as different variable dynamic controls for the corticothalamic mechanism of the frequency-dependent facilitation in PoM.Funding Agencies|European Union Regional Development Fund through the Foundation for Polish Science; National Science CenterNational Science Centre, Poland [2013/08/W/NZ4/00691]</p

The Primary Visual Cortex Is Differentially Modulated by Stimulus-Driven and Top-Down Attention.

Selective attention can be focused either volitionally, by top-down signals derived from task demands, or automatically, by bottom-up signals from salient stimuli. Because the brain mechanisms that underlie these two attention processes are poorly understood, we recorded local field potentials (LFPs) from primary visual cortical areas of cats as they performed stimulus-driven and anticipatory discrimination tasks. Consistent with our previous observations, in both tasks, we found enhanced beta activity, which we have postulated may serve as an attention carrier. We characterized the functional organization of task-related beta activity by (i) cortical responses (EPs) evoked by electrical stimulation of the optic chiasm and (ii) intracortical LFP correlations. During the anticipatory task, peripheral stimulation that was preceded by high-amplitude beta oscillations evoked large-amplitude EPs compared with EPs that followed low-amplitude beta. In contrast, during the stimulus-driven task, cortical EPs preceded by high-amplitude beta oscillations were, on average, smaller than those preceded by low-amplitude beta. Analysis of the correlations between the different recording sites revealed that beta activation maps were heterogeneous during the bottom-up task and homogeneous for the top-down task. We conclude that bottom-up attention activates cortical visual areas in a mosaic-like pattern, whereas top-down attentional modulation results in spatially homogeneous excitation

Modular Data Acquisition System for Recording Activity and Electrical Stimulation of Brain Tissue Using Dedicated Electronics

In this paper, we present a modular Data Acquisition (DAQ) system for simultaneous electrical stimulation and recording of brain activity. The DAQ system is designed to work with custom-designed Application Specific Integrated Circuit (ASIC) called Neurostim-3 and a variety of commercially available Multi-Electrode Arrays (MEAs). The system can control simultaneously up to 512 independent bidirectional i.e., input-output channels. We present in-depth insight into both hardware and software architectures and discuss relationships between cooperating parts of that system. The particular focus of this study was the exploration of efficient software design so that it could perform all its tasks in real-time using a standard Personal Computer (PC) without the need for data precomputation even for the most demanding experiment scenarios. Not only do we show bare performance metrics, but we also used this software to characterise signal processing capabilities of Neurostim-3 (e.g., gain linearity, transmission band) so that to obtain information on how well it can handle neural signals in real-world applications. The results indicate that each Neurostim-3 channel exhibits signal gain linearity in a wide range of input signal amplitudes. Moreover, their high-pass cut-off frequency gets close to 0.6Hz making it suitable for recording both Local Field Potential (LFP) and spiking brain activity signals. Additionally, the current stimulation circuitry was checked in terms of the ability to reproduce complex patterns. Finally, we present data acquired using our system from the experiments on a living rat’s brain, which proved we obtained physiological data from non-stimulated and stimulated tissue. The presented results lead us to conclude that our hardware and software can work efficiently and effectively in tandem giving valuable insights into how information is being processed by the brain

Beta activity increases in the primary visual cortex during attention trials.

<p>A. Stimulus-driven paradigm (cat B, Cx 17/1, see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145379#pone.0145379.t001" target="_blank">Table 1</a>). Left: mean FFT spectra obtained from all correct trials during the three experimental days after the behavioral criterion was reached. The visual (gray) and auditory (black) means were obtained by averaging respectively 820 and 760 spectra of 1.28 s long data epochs (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145379#sec002" target="_blank">Methods</a> for details). Right: comparison of the mean spectrum from the correct visual trials (gray; same as in the left panel) with the mean FFT from 90 epochs from incorrect trials (black). B. Anticipatory paradigm (cat E, Cx 17/2). The recorded signals were subjected to the same analysis as in A. Means were obtained from 748 and 765 spectra for correspondingly correct visual and correct auditory trials, and from 320 spectra for incorrect visual trials. In A and B, the shading around the FFT spectra indicates the SEM. The lines above the horizontal axes denote the frequencies at which significant differences were found between the spectra from the correct visual and auditory (left) or correct and incorrect visual (right) trials (Student's t-tests with FDR correction for multiple comparisons, see the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145379#sec002" target="_blank">Methods</a> section; P ≤ 0.05). An example of filtered (16–24 Hz) beta signals recorded from cat B at the beginning of two correct stimulus-driven visual and auditory trials (right and left panel, respectively) performed on the second day after the cat reached the behavioral criterion. The consecutive horizontal lines in each panel represent a continuous signal. The vertical lines separate the final part of the signal corresponding to the inter-trial period preceding stimulus onset and the start of the stimulus presentation during the trial.</p

Relative amplitude differences of the evoked potentials during high and low beta states in visual trials.

<p>EPs induced by chiasmatic stimulation during visual trials were analyzed in all recording sites and all cats in the two experimental paradigms (cf. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145379#pone.0145379.t001" target="_blank">Table 1</a>)—A stimulus driven attention, B—anticipatory attention. Each box shows the normalized percentage difference (Δ%) between the EP amplitudes calculated for the appropriate recording site: Δ% = 100% x (high − low) / low, where “high” indicates the mean amplitude of the EPs that were preceded by bursts of high beta activity and “low” refers to the mean amplitude of the EPs that were preceded by low beta activity. Black boxes = high < low, gray boxes = high > low. Below each table we present mean amplitude change (with SEM) obtained in the relevant paradigm from all available sites and significance of its difference from zero (as P value from one-sample t-test).</p

Experimental paradigms.

<p>A. In the stimulus-driven attention paradigm, the visual and auditory trials started with the cue stimulus (a light spot or a modulated noise delivered from a loudspeaker) that moved in front of the cage for 10–20 s. The spot was switched off in front of one of the doors or the noise stopped along the side wall. The transparent screen was lifted 2 s later, and the cat was allowed to open the indicated door for a food reward. Visual and auditory trials (n = 12–20 for each) were randomly intermingled. The cage was fully closed during the experiment by a removable cover (not shown). With the exception of the two semi-translucent doors on the front, the rest of the cage was opaque (the cat’s entire body was drawn only for graphical demonstration). B. During the anticipatory paradigm, the cue was either a short (1 s) diffuse flash on both doors or a white noise delivered from the front loudspeaker. The animal then anticipated the target for 8–14 s with no stimulation present, after which a small spot of light or white noise from the side loudspeaker was delivered. C. The upper trace shows a typical LFP recording in which the beta activity can be traced by eye; the filtered beta band of this record is shown beneath the LFP signal. See the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0145379#sec002" target="_blank">Methods</a> section for details.</p