A tRNS investigation of the sensory representation of time.

The understanding of the mechanisms underlying the representation of temporal intervals in the range of milliseconds/seconds remains a complex issue. Different brain areas have been identified as critical in temporal processing. The activation of specific areas is depending on temporal range involved in the tasks and on the modalities used for marking time. Here, for the first time, transcranial random noise stimulation (tRNS) was applied over the right posterior parietal (P4) and right frontal (F4) cortex to investigate their role in intra- and intermodal temporal processing involving brief temporal intervals (<1 sec). Eighty University students performed a time bisection task involving standard durations lasting 300 ms (short) and 900 ms (long). Each empty interval to be judged was marked by two successive brief visual (V) or auditory (A) signals defining four conditions: VV, VA, AV or AA. Participants were assigned to one of these four conditions. Half of the participants received tRNS over P4 and half over F4. No effect of stimulation was observed on temporal variability (Weber ratio). However, participants that were stimulated over P4 overestimated temporal intervals in the random condition compared to the sham condition. In addition to showing an effect of tRNS on perceived duration rather than on temporal variability, the results of the present study confirm that the right posterior parietal cortex is involved in the processing of time intervals and extend this finding to several sensory modality conditions.

The role of primary auditory and visual cortices in temporal processing: A tDCS approach.

AIM: Many studies showed that visual stimuli are frequently experienced as shorter than equivalent auditory stimuli. These findings suggest that timing is distributed across many brain areas and that "different clocks" might be involved in temporal processing. The aim of this study is to investigate, with the application of tDCS over V1 and A1, the specific role of primary sensory cortices (either visual or auditory) in temporal processing. METHOD: Forty-eight University students were included in the study. Twenty-four participants were stimulated over A1 and 24 participants were stimulated over V1. Participants performed time bisection tasks, in the visual and the auditory modalities, involving standard durations lasting 300ms (short) and 900ms (long). RESULTS: When tDCS was delivered over A1, no effect of stimulation was observed on perceived duration but we observed higher temporal variability under anodic stimulation compared to sham and higher variability in the visual compared to the auditory modality. When tDCS was delivered over V1, an under-estimation of perceived duration and higher variability was observed in the visual compared to the auditory modality. CONCLUSION: Our results showed more variability of visual temporal processing under tDCS stimulation. These results suggest a modality independent role of A1 in temporal processing and a modality specific role of V1 in the processing of temporal intervals in the visual modality.

Blood pressure control has distinct effects on executive function, attention, memory and markers of cerebrovascular damage.

Hypertension causes cognitive impairment, involving mainly executive functions, but the effect of blood pressure (BP) control on the different cognitive domains is still debated. We correlated executive function, attention and memory with BP control and cerebrovascular damage in 60 undemented middle-aged hypertensives at baseline and after 6-year follow-up. At first evaluation, the patients with poor BP control had higher score of white matter lesions, reduced cerebrovascular reserve capacity and greater carotid intima-media thickness (IMT) than those with good BP control. Performance on executive tests correlated with IMT and with performance on attention tests, which was impaired by low diastolic BP. At long-term follow-up, performance in attention and executive tests improved in spite of the minor improvement of BP control, increased IMT and worse memory. Low diastolic BP has a negative effect on attention, which affects executive performance at first cross-sectional examination. This confounding effect has to be taken into consideration when planning studies on cognitive function. Longitudinal studies are required to unravel the effect of BP control on cognitive function, as only long-term antihypertensive treatment improves both attention and executive performance.

P300 latency for the diagnosis of minimal hepatic encephalopathy: evidence that spectral EEG analysis and psychometric tests are enough.

BACKGROUND: No gold standard exists to detect minimal hepatic encephalopathy. Event-related evoked potentials (P300 latency) were proposed as the best tool to assess this condition. EEG spectral analysis and psychometric evaluation are also used to assess minimal hepatic encephalopathy. AIMS: The present study aims at comparing these three techniques. PATIENTS: Eighty-six cirrhotic patients without overt hepatic encephalopathy were studied. METHODS: Patients underwent EEG spectral analysis, psychometric evaluation and P300. P300 latency was age-adjusted; psychometric tests were age- and education-adjusted. Values >2Z were considered to be altered. The alteration of at least two psychometric tests was considered for cognitive impairment. RESULTS: At least one of the three indexes was altered in 61% (CI95% = 49-71) patients; EEG spectral analysis was altered in 41% (CI95% = 30-52%) patients, psychometric performance in 34% (CI95% = 24-45%) and P300 latency in 13% (CI95% = 7-22%). P300 latency was altered only in the patients having EEG spectral analysis or psychometric alterations, but for two cases. Psychometric performance and EEG spectral analysis, but not P300 latency, were correlated with indexes of liver function. CONCLUSIONS: P300 latency provided little additional information and was less related to liver function than EEG spectral analysis and psychometrical investigation.

Health related quality of life in adults with repaired tetralogy of Fallot: psychosocial and cognitive outcomes.

OBJECTIVE: To assess the health related quality of life of patients who were operated on during childhood for total correction of tetralogy of Fallot, focusing on the psychosocial and cognitive outcomes. PATIENTS: 54 patients (24 men and 30 women, mean (SD) age 32 (4) years), operated on for total correction of tetralogy of Fallot at mean age of 8.2 years, underwent a cardiological examination, psychological assessment (semistructured interview, Minnesota multiphasic personality inventory), evaluation of quality of life (36 item short form health survey), and neuropsychological assessment with an extensive neuropsychological battery of tests. RESULTS: Psychological characteristics-(1) a lower than normal academic level, (2) a job inadequate for educational level, (3) a preference for an overprotective familiar setting, and (4) a difficulty communicating own corporal image. Denial of the cardiopathy was found to be a common behaviour to normalise functioning. Very few patients had a deficit in memory, learning, or attention functions; rather, patients had a deficit in the executive functions, problem solving, and planning strategies. CONCLUSIONS: Despite a satisfactory health related quality of life, there are residual psychological and social problems in addition to impaired cognitive outcomes in the presence of a normal intelligence quotient.

Neuropsychological-neurophysiological alterations and brain atrophy in cirrhotic patients.

Psychometric performance has been reported to be related to brain atrophy in cirrhotics, but the relationship between brain atrophy and EEG findings is still unknown. The aim of this study was to ascertain the relationship among brain atrophy, EEG, and cognitive performance in cirrhotics. Sixty-eight cirrhotics (age = 55 +/- 10 years; males-66%) underwent psychometric evaluation (Symbol Digit Test, Trail Making Test-Part A, Scan test), EEG recording and spectral analysis (S-EEG), and brain CT scan. Central brain atrophy was ascertained by the following indexes of brain atrophy: the Evans' index, the bicaudate index, the cella media index, the bifrontal index, and the ventricular index; cortical brain atrophy by the sulci index. The severity of liver failure was assessed by the Child-Pugh score: 18% of patients were Child-Pugh Class A, 50% Class B, and 32% Class C. Central and cortical atrophies were found to be correlated with age, but not with the Child-Pugh score. Psychometric performance and the EEG mean dominant frequency (MDF) were found to be correlated with brain atrophy. Multivariate analysis showed that a poor psychometric performance was independently predicted by EEG slowing (MDF: p < 0.01) and by central brain atrophy (cella media index: p < 0.01). In conclusion, brain atrophy was associated with a poor psychometric performance and EEG alterations in cirrhosis. Both brain atrophy and EEG alterations independently predicted cognitive dysfunction in cirrhotic patients.

Prevalence and prognostic value of quantified electroencephalogram (EEG) alterations in cirrhotic patients.

BACKGROUND/AIMS: The electroencephalogram (EEG) is frequently altered in cirrhotic patients. We, therefore, performed a study to ascertain the features and the prognosis of cirrhotic patients without current overt hepatic encephalopathy (OHE) who have EEG alterations. METHODS: A series of 296 consecutive cirrhotic patients who had undergone quantified-EEG was studied. The median follow-up was 442 days, 128 patients had bouts of OHE and 78 patients died from liver-related causes. Another group of 124 cirrhotic patients with a median follow-up of 223 days was examined to validate the prognostic model. RESULTS: EEG alterations were detected in 38% of the patients. The prevalence of EEG alterations was associated with the severity of cirrhosis (class B: odds ratio (OR) = 2.3, 95% confidence interval (CI) = 1.2-4.7; class C: OR = 3.5, 95% CI = 1.6-7.7), but not with the aetiology (alcoholic vs. non-alcoholic: OR = 0.9; 95% CI = 0.5-1.5). The EEG predicted the occurrence of OHE (chi2 = 26; P < 0.001) and mortality (chi2 = 34; P < 0.001), also adjusting for Child-Pugh class by a multivariate analysis. In the patients with a Child-Pugh score of > or = 8, the EEG discriminated between those patients with a higher 1-year risk of OHE (hazard ratio (HR) = 3.3, 95% CI = 1.8-6.1) and death (HR = 3.1, 95% CI = 1.7-5.6). CONCLUSIONS: In conclusion, quantified-EEG had a prognostic value for the occurrence of bouts of OHE and mortality in cirrhotic patients.

Lexical and semantic processing in the absence of word reading: evidence from neglect dyslexia.

Nine patients with left-sided neglect and nine matched control patients performed three tasks on horizontal (either normal or mirror-reversed) letter strings. The tasks were: reading aloud, making a lexical decision (word vs non-word), and making a semantic decision (living vs non-living item). Relative to controls, neglect patients performed very poorly in the reading task, whereas they performed nearly normally in the lexical and semantic tasks. This was considered to be a dissociation between direct tasks, rather than a dissociation between explicit and implicit knowledge. The explanation offered for the dissociation is in terms of both a dual-route model for reading aloud and a degraded representation of the letter string.

Spatial representations of words and nonwords.

The first two experiments investigated whether the representations of words, besides being unitary, are also spatial in nature. Subjects were required to search for target letters in either five-letter words or five-letter nonwords. They were instructed to press the right-side key for one target and the left-side key for the other target. The center item of the letter string was always at fixation. Targets appeared one at a time, located at the second (left side) or the fourth (right side) position within the letter string. The results showed that: a) responses to targets within words were faster than responses to targets within nonwords (the word-superiority effect); b) responses to compatible stimulus-response pairings were faster than responses to incompatible stimulus-response pairings (the spatial compatibility, or, more precisely, the Simon effect); and c) in Experiment 2, left-side targets were responded to faster than right-side targets within nonwords (the left-right scanning effect). It was concluded that representations of both words and nonwords are spatial in nature. Experiment 3 was aimed at testing whether the spatial layout of the representations of words is always along the left-right horizontal dimension, regardless of the topographic transformation of the stimulus. The same words and nonwords used in the previous experiments were shown vertically and the subjects were required to make left-right discriminative responses to upper and lower target letters. The results showed the word-superiority effect but no spatial compatibility effects. It was concluded that the representation of a vertically presented word is vertically arranged.