Temporal unpredictability increases error monitoring as revealed by EEG-EMG investigation.

Reacting in an unpredictable context increases error monitoring as evidenced by greater error-related negativity (ERN), an electrophysiological marker linked to an evaluation of response outcomes. We investigated whether ERN also increased when participants evaluated their responses to events that appeared in unpredictable versus predictable moments in time. We complemented electroencephalographic (EEG) analysis of cortical activity by measuring performance monitoring processes at the peripheral level using electromyography (EMG). Specifically, we used EMG data to quantify how temporal unpredictability would affect motor time (MT), the interval between the onset of muscle activity, and the mechanical response. MT increases following errors, indexing online error detection, and an attempt to stop incorrect actions. In our temporally cued version of the stop-signal task, symbolic cues predicted (temporally predictable condition) or not (temporally unpredictable condition) the onset of a target. In 25% of trials, an auditory signal occurred shortly after the target presentation, informing participants that they should inhibit their response completely. Response times were slower, and fewer inhibitory errors were made during temporally unpredictable than predictable trials, indicating enhanced control of unwanted actions when target onset time was unknown. Importantly, the ERN to inhibitory errors was greater in temporally unpredictable relative to temporally predictable conditions. Similarly, EMG data revealed prolonged MT when reactions to temporally unpredictable targets had not been stopped. Taken together, our results show that a temporally unpredictable environment increases the control of unwanted actions, both at cortical and peripheral levels, suggesting a higher subjective cost of maladaptive responses to temporally uncertain events.

Electrophysiological correlates of attentional processes in patients with liver cirrhosis without minimal or clinically-overt hepatic encephalopathy.

Liver cirrhosis is often accompanied by a spectrum of cognitive deficits, labelled hepatic encephalopathy (HE). The precise specification of cognitive impairment associated with HE has not been yet elucidated. The aim of this study was an attempt to examine cortical function in cirrhotic patients using EEG event-related potentials during a demanding task involving selective attention. We compared group of 30 patients with liver cirrhosis without minimal or overt HE with education-, age- and sex-matched 29 non-cirrhotic controls. Both groups performed an attentional blink (AB) task, which requires detecting and identifying two target characters in a longer series of rapidly and sequentially presented characters. EEG signals from 32 electrodes were measured and then analyzed in the paradigm of event-related potentials (ERP). Though the groups did not differ in the detection rate of the target stimuli, ERP waveforms revealed two group differences of component amplitudes. The first difference was related to the waveform amplitude within the 200-400 ms after first target in the right frontal region (frontocentral N2 component). Moreover, in patient group this amplitude positively correlated with the blood plasma level of alkaline phosphatase and gamma-glutamyl transpeptidase. The second amplitude difference was observed in the midline parieto-occipital regions within the 400-600 ms after the first target (P3b component). The AB task and ERP analysis allowed to find differences in cortical functioning in cirrhotic patients even without overt cognitive deficits. Our finding demonstrates that liver dysfunction can influence cortical processing associated with detecting and categorizing stimulus change.

Cognitive evoked response potentials in patients with liver cirrhosis without diagnosis of minimal or overt hepatic encephalopathy. A pilot study.

Liver cirrhosis is often accompanied by cognitive deficits called minimal hepatic encephalopathy (MHE) when it is observed to a moderate extent. In the present study, brain activity and cognitive functioning were examined in patients with liver cirrhosis without MHE or overt clinical hepatic encephalopathy. A battery of neuropsychological tests and event related potentials (ERPs) were used. Moreover, an additional n-back task was administered with two difficulty levels (1- and 2-back). This task was designed to engage cognitive processes of storage and manipulation of information in working memory. The participants have to decide whether the letter shown was the same as a target (congruence condition). No significant differences were found in the performance of either the neuropsychological tests or the n-back task. However, the expected effects of decreased performance as well as a decrease in P3 amplitude with difficulty level were identified. The interaction of group x congruence condition was also observed in the P2 component time window. These results may indicate group differences manifesting in early stages of information processing in working memory. It confirms that the patients whose neuropsychological performance is within the normal range can still reveal subtle changes in CNS functioning visible in ERP research. The study confirms the usability of the ERP method in diagnosis of neurocognitive functions in patients with liver cirrhosis, which seems to be more sensitive than neuropsychological tests.

Event-related cerebral potentials for the diagnosis of subclinical hepatic encephalopathy in patients with liver cirrhosis.

PURPOSE: Subclinical hepatic encephalopathy (SHE) seems to be a common problem in liver cirrhosis, however, studies assessing the pathogenesis of this disease remain unclear. Currently no gold standard exists for the diagnosis of this complex neuropsychiatric syndrome. The present study was undertaken firstly to examine the diagnostic usefulness of auditory event-related cerebral potentials (ERPs) in the detection of SHE, and secondly to compare it with that of the most validated psychometric test. MATERIAL AND METHODS: 22 patients with liver cirrhosis without overt hepatic encephalopathy and 28 healthy controls were studied, using auditory ERPs. In addition they underwent a battery of neuropsychological and laboratory tests. RESULTS: P300 latency analysis turned out that cirrhotics patients had significantly longer P300 latency than controls. The only neuropsychological test showing significant difference between clinical and control group was the similarities subtest of WAIS-R. CONCLUSIONS: The results of the present study suggest that ERPs are more sensitive method than psychometric tests in detecting early changes in the brain function of patients with cirrhosis and for this reason this neurophysiological method should be applied in clinical practice.

Suppressive effect of NMDA receptor antagonist MK-801 on nocturnal serotonin N-acetyltransferase activity in the rat pineal gland.

Treatment of rats at night with a non-competitive NMDA receptor antagonist MK-801 (0.025-1 mg/kg, i.p.) produced a dose-dependent decrease in the nocturnal activity of the pineal serotonin N-acetyltransferase (NAT), the rate limiting enzyme in melatonin biosynthesis. A maximal inhibition (by 67-75%) of the enzyme activity was observed after the drug doses of 0.1 mg/kg in female rats, and 1 mg/kg in male animals. The data suggest that the NMDA receptor-mediated glutamatergic neurotransmission is a step necessary for NAT induction (and melatonin biosynthesis) in the mammalian pineal gland.