Biomedical subjects

Sami Schiff

Publications and source records attributed to Sami Schiff.

5 recordsLinked to original sources

PubMed2006

Top-down and bottom-up processes in the extrastriate cortex of cirrhotic patients: an ERP study.

OBJECTIVE: This study aims to evaluate the efficiency of top-down and bottom-up processes in the extrastriate cortex of cirrhotic patients without overt hepatic encephalopathy (HE). METHODS: Reaction times (RTs), accuracy and event-related potentials (ERPs) were recorded during the execution of a visual Simon task in 17 cirrhotic patients and 10 healthy controls. Amplitude and latency of the P1 and N1 (indexes of bottom-up processes) and of the N2pc (index of top-down processes) were measured. RESULTS: Patients were slower than controls, and patients with minimal HE (MHE) were slower than patients without MHE. The distribution analysis of RTs showed that the Simon effect decays with slower RTs in all the groups and that the shape of the distribution was different in MHE patients. No differences were found between cirrhotic patients and controls for P1 and N1 amplitude and latency. In contrast, N2pc latency was delayed in cirrhotic patients compared to controls independently of MHE. CONCLUSIONS: In the extrastriate cortex of cirrhotic patients without HE, top-down processes are altered whereas bottom-up processes are preserved. SIGNIFICANCE: The analysis of exogenous and endogenous visual components of ERPs provides a model to study the functional dissociation between top-down and bottom-up processes inside the extrastriate cortex.

Brain↗

PubMed2005

Diagnostic tools for the study of vascular cognitive dysfunction in hypertension and antihypertensive drug research.

Arterial hypertension is one of the main risk factors for cerebrovascular diseases, and antihypertensive treatment has significantly reduced their associated mortality. However, morbidity has not been reduced to a similar extent and a still increasing number of patients suffers from recurring strokes and from the disabling consequences of cerebrovascular diseases and develops progressive cognitive impairment. It is still debated to what extent antihypertensive treatment may prevent the development of cognitive dysfunction, due to the lack of a focused approach to vascular cognitive impairment, to the lack of a systematic study of the early phases of dementia, and to the use of diagnostic tests that are not sensitive and specific for a slow onset clinical condition, such as dementia. The aim of the present expert consensus report is to enlist the diagnostic tools that are currently available to assess mild cognitive impairment (MCI) and early dementia and that are sensitive and specific enough to be used in observational, longitudinal, and interventional clinical research studies, aiming to investigate the impact of antihypertensive drugs on vascular dementia (VD).

Animals↗

PubMed2005

Attention dysfunction in cirrhotic patients: an inquiry on the role of executive control, attention orienting and focusing.

Attention alterations are reported in cirrhotics. Aiming at clarifying attention functioning in cirrhotics, an inquiry on the functioning of the anterior (AAS) and the posterior (PAS) attention system was performed. Thirty-six cirrhotics without overt hepatic encephalopathy (24 with EEG or TMT-A alterations) and 16 matched control subjects were enrolled. The AAS was studied by the Stroop task measuring selective attention control, the PAS was studied by the Posner task and the Focus task measuring automatic covert orienting and visual focusing of attention respectively. Cirrhotics presented a task-dependent psychomotor slowing (Stroop > Posner > Focus) with an increased percentage of errors in the incongruent condition of the Stroop task [F(1, 57) = 4.9, p < 0.03]. Class C patients had both a selective slowing [F(1, 33) = 4.3, p < 0.05] and an increased percentage of errors in the incongruent condition [F(1, 34) = 5.1, p < 0.05] compared to Class A-B patients and controls. The patients with an altered EEG performed the Stroop test significantly slowly than those without EEG alterations [F(1, 41) = 8.9, p < 0.01] and with a clear trend for a higher number of errors in the incongruent condition [F(1, 39) = 3.8, p < 0.06]. In contrast, attention orienting and focusing were maintained. In conclusion, the AAS is more sensitive than the PAS to the early stages of hepatic encephalopathy.

Attention↗

PubMed2005

Impairment of response inhibition precedes motor alteration in the early stage of liver cirrhosis: a behavioral and electrophysiological study.

Abnormality in movement initiation may partially explain psychomotor delay of cirrhotic patients, even in the absence of overt hepatic encephalopathy (HE). Therefore, the aim of this study was to determine the mechanisms of psychomotor delay observed in patients with cirrhosis in the absence of overt HE. Fourteen patients with nonalcoholic cirrhosis and 12 healthy matched control subjects underwent the lateralized readiness potential (LRP) measurement elicited by a visuospatial compatibility task (Simon task). Stimulus-triggered LRPonset reflects the time in which response is selected, while response-triggered LRP onset reflects motor execution. Cirrhotic patients showed delayed reaction times (RTs) compared to controls, particularly those with trial-making test A (TMT-A) or electroencephalogram (EEG) alterations. Stimulus-triggered LRP onset was found to be delayed in cirrhotic patients compared to controls, with a significant Group-versus-Condition interaction, showing a reduced cognitive ability to cope with interfering codes, even in patients without minimal HE (MHE). Response-triggered LRP was found to be delayed only in the patients with TMT-A or EEG alterations. In conclusion, cirrhotic patients without overt HE display a psychomotor slowing, depending first lyon response inhibition and only later accompanied by impaired motor execution.

Data Interpretation, Statistical↗

PubMed2005

Horizontal and vertical Simon effect: different underlying mechanisms?

Reaction times are usually faster when stimulus and response occur at the same location than when they do not, even if stimulus location is irrelevant to the task (Simon effect). This effect was found with both horizontal and vertical stimulus-response arrangements. The same mechanisms have been proposed to be involved in either case. Here, we compared a horizontal and a vertical Simon task by means of a RT time-course analysis of the Simon effect. Also, we analysed the lateralised readiness potential (LRP), an index of covert response-preparation processes. In the horizontal task, the Simon effect decays over time and pre-activation occurs above the motor cortex ipsilateral to the stimulus. In contrast, the Simon effect does not decay over time and no early incorrect LRP deflection is observed in the vertical task. These findings suggest that typical activation accounts can fit only the horizontal Simon effect, while a translation explanation is more suitable for the vertical Simon effect.

Adult↗