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1
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Interactions between P300 and passive probe responses differ in different visual cortical areas

100%
Michalski A.
Acta Neurobiologiae Experimentalis
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2001
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vol. 61
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issue 2
93-104
EN
The regulation of firing thresholds of cortical neurons was suggested as one of the mechanisms underlying the generation of the P300 component in the human event-related potential. According to this hypothesis, the detection of an important stimulus produced the widespread inhibition of ?irrelevant? networks, interrupting their ongoing activity and facilitating the analysis of selected information. In the present experiment, the responsiveness of visual cortex was evaluated during the P300 potential by using additional, probing stimuli. Large separation of the cortical visual fields permitted separate analysis of the input and more advanced stages of processing. Responses were recorded from Fz, Cz, Pz and Oz scalp sites. P300 waves were evoked by visual, mentally counted stimuli in a standard 'odd-ball' procedure. Visual probes were delivered 200, 300, 400, 500, 700 and 1000 ms later. No responses to the probes were required. Significant suppression of responses to the probes delivered less than 400 ms after target stimuli was found in Oz and Pz but not in Cz or Fz . The suppression was not proportional to the voltage levels from which probe responses started. In Fz and Cz, latencies of probe responses were elongated if probes were delivered less than 400 ms after target stimuli. The results suggest that probe responses suppressed by the P300 potential in occipital and parietal cortex may be restored in frontal areas. In these areas the P300 potential could delay probe responses instead of suppressing them.
2
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Expectation of an important event affects responses to irrelevant stimuli of different modalities

100%
Michalski A.
Acta Neurobiologiae Experimentalis
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2000
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vol. 60
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issue 4
467-478
EN
Periodic alterations of event-related potentials (ERPs) were studied during 'oddball' tasks. Sequences of randomly intermixed frequent (non-target) and rare (target) stimuli were presented. In visual experiments, these were flashes of light of two different colors. In auditory tests there were two tones of different frequencies. The instruction was to keep a mental count of each target stimulus. To study the alterations of the 'state of the brain' produced by target detection, responses to non-targets immediately following targets were compared with responses to an eighth subsequent non-target stimulus. To evaluate the effect of such 'brain states' on responses to stimuli of a different modality, additional visual stimuli (probes) were delivered after both auditory and visual 'oddball' stimuli. It was found that responses to the eighth presentation of non-target stimulus were preceded by significant negative shift of recorded potential. This shift was smaller before the responses to non-targets immediately following the presentation of target stimuli. The difference was significant both in auditory and visual tests. Responses to 'oddball' stimuli were little affected: only the reduction of P200 peaks in 'after target' responses was significant in visual tests. Responses to probes showed stronger effects: when visual probes followed visual 'oddball' stimuli, all three components measured (N100, P130 and P200) were shifted positively in responses to eighth presentations of non-targets. When visual probes were presented in auditory tests, only the amplitude of the N100 component was significantly affected.
3
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Novel environment as astress- -inducing factor. An event-related potentials study

100%
Michalski A.
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vol. 58
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issue 3
199-205
EN
The effect of stress induced by the novelty of a situation was evaluated by means of event-related potentials (ERPs). Potentials, recorded with Fz, Cz and Pz electrodes, were evoked by flashing red and yellow LED diodes. A standard 'odd ball' procedure was used, in which flashes of one color were mentally counted (target stimuli). ERPs evoked by target and non-target stimuli recorded in the first session of the experiment were compared with those recorded at least 40 min later. The early waves and P200 components indicated the increased responsiveness during the initial sessions. Amplitudes of both components were significantly larger. Latencies of the early waves were also significantly shorter. The effects were present in responses to both target and non-target stimuli. In contrast, the latency of P300 wave was significantly elongated during the first recording. Grand-averaged curves indicated also a reduction of P300 amplitude, but when individual waves were analyzed, the effect did not reach the level of statistical significance. It was suggested that the novel situation could be employed as a model of relatively pure stress, useful in the interpretation of other results such as the effects of pain.
4
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The effect of tonic pain on processing the non-painful stimuli indexed by late components of event-related potentials

100%
Michalski A.
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vol. 58
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issue 1
55-64
EN
Event-related potentials (ERPs) evoked by light flashes and auditory tones in a standard odd-ball procedure were recorded from Fz, Cz and Pz scalp sites. Tonic pain was evoked by immersion of the hand in cold water (5oC). Significant effects of pain were found in responses to target stimuli but not in responses to non-target stimuli. P300 wave was affected more than the earlier P200 component. The reduction of P300 amplitude was the strongest effect, both in auditory and visual tests. P300 latency was not significantly affected. Difference curves (target minus non-target ERPs) showed the additional effects: latency of P200 component was elongated and its amplitude enlarged but only in auditory experiments. In control experiments with warm water stimulation no significant alterations of P300 or P200 components were found. The results show that the effect of tonic pain is specific: it predominantly affects the processes that manifest themselves as amplitude changes of P300 components in responses to target stimuli.
5
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Cortical responsiveness is reduced during P300 potential. Does the level of initial activity affect this inhibition?

63%
Milner R., Michalski A.
Acta Neurobiologiae Experimentalis
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2003
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vol. 63
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issue 4
351-360
EN
The regulation of firing thresholds of cortical pyramidal cells has been suggested as one of the mechanisms underlying the generation of the P300 component of the human event-related potential. According to this hypothesis, the detection of an important stimulus produces a widespread inhibition of 'irrelevant' networks, interrupting the ongoing cortical activity and facilitating the analysis of the important information. In the present experiment, target stimuli in a standard 'odd-ball' paradigm were used as important events. The cortical responsiveness was measured using the responses to additional probing stimuli delivered 400 ms and 1,000 ms after target and non-target stimuli. The subjects were asked to count mentally the target stimuli and ignore the non-targets and the probes. The level of 'irrelevant' cortical activity was manipulated using additional visual noise stimulation. Event-related potentials were recorded at Fz, Cz, Pz and Oz scalp sites. Our results showed that the noise reduced the initial responses to target and non-target stimuli in Oz, Pz and Cz but not in Fz recordings. The noise reduced the probe responses in Oz and Pz but not in Cz and Fz recordings. The amplitudes of P300 components were not affected by the noise. The target stimuli reduced the subsequent probe responses in Pz and Cz but not in Oz and Fz recordings. Thus, the effects of noise and target detection were not identical in the different regions of cortex. The other important outcome of our study was that the target stimuli suppressed the effects of noise. The effect of noise on probe responses was significant in the non-target but not in the target trials. The effect of noise was significant if the probes were delivered 1,000 ms after 'odd-ball' stimuli, but it was insignificant when the delay was only 400 ms. Such results support the hypothesis that important information reduces cortical responses to other, irrelevant stimuli.
6
Content available remote

The effects of glutamate ionophoresis on single cell responses and inter-neuronal interactions in the kitten visual cortex

63%
Michalski A., Kraszewski K.
Acta Neurobiologiae Experimentalis
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1995
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vol. 55
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issue 2
85-97
EN
There was studied the effect of glutamate micro-ionophoresis on visual responses (PSTHs) and cross-correlograms of neurones recorded simultonously in the cortex of 4-6 week old kittens.PSTHs and cross-correlograms were tested before,during and after glutamate injections and compared with adult cats data from previous experiment.
7
Content available remote

Correlated activity of lateral geniculate neurones in binoculary deprived cats

63%
Michalski A., Wrobel A.
Acta Neurobiologiae Experimentalis
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1994
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vol. 54
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issue 1
3-10
8
Publication available in full text mode
Content available

Fabrication, Structure and Consolidation of NiAl-Al_2O_3 Mechanically Alloyed Nanocomposite Powders

51%
Oleszak D., Michalski A., Majewski T.
Acta Physica Polonica A
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2002
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vol. 102
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issue 2
187-192
EN
Reactive milling of NiO + Al powder mixture resulted in the formation of NiAl-Al_2O_3 nanocomposite powders, with a crystallite size of about 20 nm. The Hall-Williamson analysis revealed that NiAl showed an orientation dependent crystallite size after short processing time and orientation dependent internal strain after long milling time. Both anisotropies were removed by heating the powders in the differential scanning calorimetry. Calorimetric studies showed one exothermic effect attributed to the reduction reaction of NiO and endothermic one associated with melting of Al. Two methods were applied for powders compaction: resistance sintering and pulse electric discharge. In both cases the densities of about 90% of the theoretical value were achieved. A significant increase in average NiAl crystallites size in compacted samples was observed, up to several hundreds of nanometers.
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