Márk Molnár

Evoked potential correlates of stimulus deviance during wakefulness and sleep in cat — animal model of mismatch negativity

Auditory evoked potentials (EPs) elicited by standard (STs) and deviant tones (DTs) of different probabilities were studied in freely moving cats during wakefulness and sleep. A large double peaked negativity, so-called mismatch negativity (MMN), was evoked by the unattended low probability DTs. The EPs recorded from the AI and AII areas of the auditory cortex showed more dynamic changes than the vertex and association cortical responses. The amplitude of the MMN was inversely proportional to the probability of DTs. The latency of the MMN showed dependence both on the location of the recording site and on the probability of DTs. During slow wave sleep (SWS) the MMN of increased latency could be evoked only at the lowest probabilities. The cortical distribution of the MMN changed in the SWS.

Auditory Evoked Potentials Reflect Serotonergic Neuronal Activity—A Study in Behaving Cats Administered Drugs Acting on 5-HT1A Autoreceptors in the Dorsal Raphe Nucleus

A valid indicator of central serotonergic neurotransmission would be useful for various diagnostic and psychopharmacological purposes in psychiatry. However, known peripheral serotonergic measures only partially reflect serotonergic function in the brain. Previous findings suggest that the intensity dependence of auditory evoked potentials (AEPs) is closely related to central serotonergic activity. The present study examines the effects of microinjection of a 5-HT1A agonist (8-OH-DPAT) and a 5-HT1A antagonist (spiperone) into the dorsal raphe nucleus (DRN) on AEP recorded epidurally from the primary and secondary auditory cortex in behaving cats. We found a stronger intensity dependence only of AEP from the primary auditory cortex after 8-OH-DPAT, which inhibits the firing rate of serotonergic DRN neurons, and a weaker intensity dependence after spiperone, which increases serotonergic cell firing, as compared to baseline measurements. These results demonstrate that the intensity dependence of AEP is inversely related to serotonergic neuronal activity and that it may be a promising tool for assessing central serotonergic function in humans (e.g., identifying patients with low serotonergic neurotransmission).

Microwave-assisted conversion of carbohydrates to levulinic acid: an essential step in biomass conversion

Degradation of non-edible carbohydrates to levulinic acid (4-oxopentanoic acid) was studied by using dielectric heating with microwave energy. Levulinic acid and its reduced and dehydrated derivative, γ-valerolactone (GVL), can be used for the production of small-molecule, functionalized hydrocarbons, which might be potential platform molecules for the chemical industry. First, simple model compounds (fructose, glucose, saccharose and cellobiose) were hydrolyzed in order to find the optimum reaction conditions (e.g. reagent, reaction temperature, acid concentration, time) for the degradation and transformation of polysaccharides (cellulose, chitin, chitosan) by using controlled microwave irradiation. Cellulose, a non-edible biopolymer of plant origin, was successfully converted to levulinic acid under the optimized conditions (2 M H2SO4, 170 °C, 50 min) with a yield of 34.2% in a mono-mode Multisynth microwave reactor. The reactions proceeded with hydrochloric acid catalysis as well, and a slightly better yield was achieved, however, using HCl (a chlorine containing catalyst) raises serious environmental concerns. The hydrolysis of glucosamine-based glycans (D-glucosamine, N-Ac-D-glucosamine, LMw-chitosan, MMw-chitosan, chitin) was also studied and optimized with sulfuric acid as a catalyst in a mono-mode Multisynth microwave reactor. The highest yield of levulinic acid was obtained with 2 M H2SO4 at 190 °C for 30 min. N-Ac-D-glucosamine, D-glucosamine, LMw-chitosan and MMw-chitosan resulted in levulinic acid with yields between 20.6% and 32.7%, the larger molecular weight chitin was degraded to levulinic acid with a yield of 37.8%.

The point correlation dimension: performance with nonstationary surrogate data and noise.

The dynamics of many biological systems have recently been attributed to low-dimensional chaos instead of high-dimensional noise, as previously thought. Because biological data are invariably nonstationary, especially when recorded over a long interval, the conventional measures of low-dimensional chaos (e.g., the correlation dimension algorithms) cannot be applied. A new algorithm, the point correction dimension (PD2i) was developed to deal with this fundamental problem. In this article we describe the details of the algorithm and show that the local mean PD2i will accurately track dimension in nonstationary surrogate data.

On the origin of the P3 event-related potential component

Human findings indicate that the most important brain regions in the electrogenesis of the P3 event-related potential component are the junction of the parieto-temporal lobes, parts of the limbic system and some parts of the thalamus. Data collected in animal experiments support the results of the human studies emphasizing the role of the association cortical areas, that of limbic structures and possibly of some thalamic nuclei. It is not clear as yet how the activity of these hypothesized generators are integrated and to what extent, and how they contribute to the scalp-recorded P3.

Steady-state responses from the cat auditory cortex

Responses to 350 ms trains of clicks with 10-100 Hz repetition rate were recorded from the auditory cortices of six cats. Click trains of 30-50 and 90-100 Hz elicited a clear steady-state response (SSR) in awake state. SSRs were small or absent below 30 Hz and in 60-70 Hz stimulus range. In slow wave sleep the optimal rate to elicit SSR shifted towards lower frequencies. 90 Hz SSR was largest in paradoxical sleep. SSRs were strongly suppressed by barbiturate anesthesia. The amplitude of the SSR from the medial geniculate body (MGB) in two cats gradually decreased from 20 to 100 Hz and was more resilient to barbiturate anesthesia than the cortical SSRs. Only low amplitude or no SSRs could be recorded from vertex, visual and association cortices and from the hippocampus in control recordings. The results suggest different generation mechanisms for SSRs recorded from cat auditory cortex and MGB. Human auditory SSRs resemble cat auditory cortical SSRs more than those recorded from cat MGB. The results imply that auditory SSRs in humans are generated in the cortex.

Rhodium-catalyzed hydrogenation of olefins in γ-valerolactone-based ionic liquids

γ-Valerolactone-based ionic liquids were successfully used as the catalyst phase for [Rh(cod)2][BF4]/RP(C6H4-m-SO3Na)2 (R = Me, Pr, Bu, Cp) catalyzed hydrogenation of different olefins. Compared to broadly used ionic liquids e.g. 1-butyl-3-methylimidazolium chloride [bmim][Cl], the turnover frequencies were significantly higher and the reaction was selective for the CC double bonds in the presence of carbonyl, cyano, and phenyl groups. The catalyst was recycled for ten consecutive runs under regular or biphasic conditions without loss of activity. The vapour pressure and viscosity of γ-valerolactone-based ionic liquids were determined as well.

Spectral and complexity features of the EEG changed by visual input in a case of subcortical stroke compared to healthy controls

OBJECTIVE To compare spectral and complexity characteristics of the EEG in a unique case of subcortical infarct to those seen in healthy controls. METHODS Absolute and relative frequency spectra, theta/beta ratio, the brain symmetry index (BSI), Omega-complexity and synchronization likelihood were calculated of the EEG recorded in eyes closed and eyes open conditions. RESULTS Increased absolute delta, theta, and Omega-complexity in these frequency bands, higher theta/beta ratios, and decreased relative beta activity were found in the side of the infarct. The BSI localized the excess of slow, and decrease of fast frequency activity to the area of ischemia. Following eyes opening the increase of fast and decrease of slow frequencies, the increase of Omega-complexity in the alpha and beta bands, and the decrease of synchronization likelihood for the fast frequency bands were reduced in the side of the infarct. CONCLUSIONS The subcortical infarct caused ipsilaterally increased slow, and decreased fast frequency activity accompanied by decreased synchronization of slow, increased synchronization of fast frequencies. Reduced reactivity in the ischemic side was particularly apparent for complexity measures. SIGNIFICANCE Complexity indices of the EEG are sensitive complementary measures of electrophysiological changes caused by local lesions such as subcortical stroke.

Intensity dependence of auditory evoked potentials in behaving cats

The intensity dependence of auditory evoked potentials (AEPs) recorded epidurally over the primary (AI) and secondary (AII) areas of the auditory cortex was studied in behaving cats during wakefulness, sleep and anesthesia. Four kHz tones of 50, 60, 70, and 80 dB SPL, presented in random order every 2 +/- 0.2 s by a bone conductor, elicited clear changes of the AEP amplitudes with increasing stimulus intensity, but individual components displayed different response curves. AEP components from the AI region showed saturation of their amplitude with stimulus intensity (P13, P34) or no amplitude increase (N19), while amplitude and intensity were linearly related in the AII area. The intensity dependence of the first positive component (P12/P13) was consistently stronger for the AEP recorded from the AI than from the AII area, while later components exhibited no difference between AI and AII. During slow wave sleep, the intensity dependence of this first positive component increased in the two areas, while that of later components decreased. Pentobarbital anesthesia abolished almost all later components and depressed the intensity dependence of the first positive component both in the AI and AII area. These results indicate that (I) clear intensity dependence of AEP exists in the cat auditory cortex and (2) this intensity dependence, especially that of the first positive AEP component, shares functional similarities to the human augmenting/reducing phenomenon in the auditory modality concerning regional differences and sleep-waking cycle.

Towards the Possible Clinical Application of the Mismatch Negativity Component of Event-Related Potentials

The mismatch negativity (MMN) is an event-related potential component that signifies neurophysiological processing of fine acoustic differences. The MMN indicates attention-independent change detection, reflects auditory sensory memory and provides a physiological measure of difference sensitivity. This paper will provide an overview of current research where results gained by MMN testing in different patient groups were central to the interpretation of an assumed abnormality of processing or storing acoustic features.