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Biomedical subjects

P Nichelli

Publications and source records attributed to P Nichelli.

At least 19 recordsLinked to original sources
PubMed1996

Time perception in a neglected space.

We have studied the distortion of perceived time in a patient with left neglect. This patient consistently over-estimated the duration of stimuli in the neglected space. Overestimation was observed both with an interval comparison (300/700 ms) and with a time production (1 s) paradigm. We suggest that encoding duration in the hundreds of milliseconds range is a process based on an internal clock mechanism. The functioning of that clock varies as a function of the processing load.

Attention↗
PubMed1996

Accidental choke-cherry poisoning: early symptoms and neurological sequelae of an unusual case of cyanide intoxication.

We report the case of a 56-year-old woman who was accidentally poisoned when she ingested choke cherries whose pulp contained cyanide, and describe the acute clinical picture, the neurological sequelae and the neuroradiological findings. After recovery from coma, the patient showed signs of a parkinsonian syndrome, retrobulbar neuritis and sensory-motor neuropathy. MRI showed abnormal signal intensities involving the basal ganglia. Since no memory deficits were observed, we argue that the parkinsonian syndrome was caused by cyanide intoxication rather than by subcortical damage due to hypoxia.

Amygdalin↗
PubMed1996

Perceptual timing in cerebellar degeneration.

This study examined time perception in 12 patients with cerebellar degeneration (CD) and in 13 normal controls (NC). We used a time bisection procedure with four interval conditions (100-900 msec; 8-32 sec; 100-600 msec; 100-325 msec). Each subject's bisection point, discrimination ability (the Weber ratio) and precision (the inverse of the proportion of unexplained variance) was calculated for each condition. CD patients' performance on the 100-900 msec time bisection condition suggested a possible time discrimination deficit, which was confirmed with intervals in the range of 100-600 msec. Time discrimination was normal on the 100-325 msec condition and impaired on the 8-32 sec bisection task. However, when discriminating long intervals, CD patients also showed a precision deficit, which points to impaired sustained attention and/or decision processes. Our findings corroborate the view that cerebellar timing processes are not limited to the motor system but are also used in perceptual computations.

Adult↗
PubMed1995

Where the brain appreciates the moral of a story.

To identify the distributed brain regions used for appreciating the grammatical, semantic and thematic aspects of a story, regional cerebral blood flow was measured with positron emission tomography in nine normal volunteers during the reading of Aesop's fables. In four conditions, subjects had to monitor the fables for font changes, grammatical errors, a semantic feature associated with a fable character, and the moral of the fable. Both right and left prefrontal cortices were consistently, but selectively, activated across the grammatical, semantic, and moral conditions. In particular, appreciating the moral of a story required activating a distributed set of brain regions in the right hemisphere which included the temporal and prefrontal cortices. These findings emphasize that story processing engages a widely distributed network of brain regions, a subset of which become preferentially active during the processing of a specific aspect of the text.

Attention↗
PubMed1995

Relations between attentional and intentional neural systems.

This study explored whether preparing an arm movement influences detection of a visual stimulus. We cued subjects to respond with either a rightward or a leftward movement to the appearance of a stimulus located either in the centre, in the left, or in the right visual field. Programming a movement toward a lateral direction enhanced visual attention at that side. Rightward movements were associated with an attentional cost only for responses to a central location, while leftward movements slowed response latencies to both central and right-sided stimuli. We hypothesized that programming a rightward movement depends on the activation of intentional centers in either cerebral hemisphere. On the contrary, leftward movements might be only driven by the contralateral hemisphere.

Adult↗
PubMed1994

Induction of a recall deficit by rapid-rate transcranial magnetic stimulation.

We used rapid-rate, repetitive transcranial magnetic stimulation (rTMS) for the noninvasive study of verbal recall. Five right-handed normal subjects were studied. Recall followed immediately after presentation of a 12-word list. Focal rTMS was applied with a figure eight coil in trains of 500 ms duration to F7, F8, T5, T6, P3, P4, or O1, O2 at latencies of 0, 250, 500, or 1000 ms during word list presentation. Recall was consistently significantly diminished only after left mid-temporal and bilateral dorsofrontal rTMS at both 0 and 250 ms latencies. We conclude that rTMS may be useful as a non-invasive tool for the study of verbal memory processes.

Adolescent↗
PubMed1994

Implicit and explicit memory in patients with Parkinson's disease with and without dementia.

OBJECTIVE: To study explicit and implicit memory processes in patients with Parkinson's disease. DESIGN: Case-control design. All subjects were given a neuropsychological test battery, and the test scores were compared among the groups. SETTING: Government-funded research facility. All subjects were examined as outpatients. PATIENTS: We tested nondemented (n = 13) and demented (n = 5) patients with Parkinson's disease and normal controls (n = 12) matched for age, gender, and educational level. MAIN OUTCOME MEASURES: Memory for verbal and pictorial stimuli under both explicit and implicit retrieval conditions. RESULTS: Both nondemented and demented patients with Parkinson's disease exhibited impairment on tests of explicit memory. Their impairment could be graded based on the level of effort required by the task: impaired free recall in nondemented patients and impaired free recall, cued recall, and recognition in demented patients. By contrast, neither group showed evidence of impairment on automatic (modality monitoring and word frequency estimation) or implicit (word and picture fragment identification) memory tasks. Correlation analyses did not support any association between the effortful memory deficits and neurologic variables, mood, or performance on executive function tests. CONCLUSIONS: Memory deficits in patients with Parkinson's disease primarily involve the conscious, effortful strategic aspects of searching long-term memory.

Aged↗
PubMed1994

Pharmacological evaluation of the cholinergic system in progressive supranuclear palsy.

Severe cholinergic loss occurs in the brains of patients with progressive supranuclear palsy. To evaluate the functional implications of this neuronal deficit, dose-response curves were obtained in patients with progressive supranuclear palsy and normal control subjects undergoing intravenous cholinergic blockade (scopolamine) and stimulation (physostigmine). Physostigmine had no significant neurobehavioral effects at any dose in patients with progressive supranuclear palsy. Scopolamine, at low and medium doses, significantly impaired memory performance of both groups, but worsened the gait of only the patients. High-dose scopolamine, which could not be tolerated by the patients, resulted in gait deterioration among control subjects. Thus, patients with progressive supranuclear palsy have increased sensitivity to cholinergic blockade compared to control subjects. Since loss of cholinergic neurons appears to contribute to the pathogenesis of certain cognitive and motor deficits found in progressive supranuclear palsy, the use of oral anticholinergics should ordinarily be avoided in this disorder. On the other hand, physostigmine at clinically tolerated dose levels seems to be therapeutically ineffective.

Aged↗
PubMed1994

Agreement in the clinical diagnosis of dementia: evaluation of a case series with mild cognitive impairment.

Interobserver agreement in the clinical diagnosis of dementia among four neurologists was evaluated. The physicians, masked to the original diagnoses, independently reviewed the clinical records of 50 outpatients consulting either the 1st University Neurology Department of Milan or the Neuropsychology Unit of the Medical Center of Veruno (Novara) for suspected cognitive impairment, during a 6-month period. The records contained patients' medical and neurological history, results of neuropsychological testing, laboratory tests, cerebral computed tomography and other investigations. For each patient, the raters had to provide both a diagnosis concerning the presence or absence of dementia and to assign an analytical diagnosis to all the dementia cases. The kappa statistic was used as a measure of interrater reliability. The level of agreement on the primary diagnosis of dementia was moderate (kappa = 0.49); with respect to the nosological diagnoses, the kappa values ranged from 0.16 for depression to 0.80 for multi-infarct dementia.

Aged↗
PubMed1994

Induction of visual extinction by rapid-rate transcranial magnetic stimulation of parietal lobe.

We used repetitive, rapid-rate transcranial magnetic stimulation (rTMS) for the noninvasive study of visual attention in humans. Six right-handed volunteers completed eight blocks of 20 single- and 10 double-visual-stimulus trials. The visual stimulus was a single asterisk on the right or left side of a computer screen or two asterisks presented simultaneously. The subject had to respond to the stimulus by pressing the right or left response key or both keys simultaneously. During six of the blocks, we applied focal rTMS in trains of five pulses at 25 Hz and 115% of the subject's motor threshold intensity to scalp positions O1, O2, P3, P4, T5, or T6. Occipital rTMS led to a large number of misses of the contralateral asterisk regardless of whether a single or double stimulus was presented. Parietal rTMS did not induce misses of single stimuli but led to a large number of misses of the contralateral asterisk in the double-stimulus condition. The effects of temporal rTMS were inconsistent. We conclude that rTMS to the occipital lobe causes a sensory detection block, whereas rTMS to the parietal lobe can induce selective extinction of contralateral visual stimuli during a simultaneous double stimulus.

Adolescent↗
PubMed1994

No specific effects of caloric stimulation on the visual-imagery processes of normal subjects.

Recent research indicates that neglect can be temporarily, but only partially, ameliorated by activating the contralateral hemisphere via caloric stimulation and other techniques. In this study, we evaluated whether caloric stimulation could be used to manipulate visual-imagery processes in normal subjects. 11 normal subjects participated in a quantitative visual-imagery task while undergoing caloric stimulation. Neither side of report nor ear of caloric stimulation affected performance. Possible reasons for this negative result are reviewed.

Adult↗
PubMed1993

Horizontal and vertical neglect dyslexia.

This case study concerns a 25-year-old right-handed male patient (G.G.) with post-traumatic lesions involving the right temporal and occipital lobe as well as the basal forebrain of the same side. G.G., who had a visual field defect almost limited to the upper left quadrant, showed both left horizontal and lower vertical neglect dyslexia, disproportionately severe when compared with left and lower visuo-spatial neglect. This is the first case report of a patient whose neglect dyslexia for vertical stimuli depended upon stimulus orientation, i.e., errors affected the final letters of top-down words and the initial letters of the bottom-up ones. This implies that neglect dyslexia can affect the internal letter shape map not only along the horizontal, but also along the vertical axis.

Adult↗
PubMed1993

Precision and accuracy of subjective time estimation in different memory disorders.

The aim of this study was to evaluate how different memory disorders affect subjective time durations. For this purpose we studied prospective time estimations in 4 amnesic (A) and in 15 Alzheimer's disease (AD) patients, and compared their performance with that of 5 matched young normal controls (YC) and 15 elderly subjects (EC). For the short-time durations we asked the subject to repeatedly reproduce a standard interval of 1 s. To test how subjects evaluated longer time durations, we choose a verbal estimation procedure. The subjects' task was to read either 5, 10, 20, or 40 digits appearing one at a time, while concurrently keeping the rhythm of 1 key press per second. At the end of each sequence, subjects had to judge the elapsed time from the beginning of the trial. Results showed that amnesics can correctly reproduce 1-s intervals. However, their accuracy of verbal estimates of longer durations was severely impaired. AD patients showed increased variability on repeated reproduction of 1-s intervals and were both inaccurate and imprecise in their verbal estimate of longer durations. Using the framework of the Scalar Timing Model, we conclude that amnesic patients exhibit a deficit in encoding and storing the current time for intervals that exceed their short-term memory range, while AD patients show a pattern of deficit that is explained by a more widespread involvement of both the clock, the memory, and the decisional mechanisms.

Adult↗
PubMed1993

Anarthria impairs subvocal counting.

We studied subvocal counting in two pure anarthric patients. Analysis showed that they performed definitively worse than normal subjects free to articulate subvocally and their scores were in the lower bounds of the performances of subjects suppressing articulation. These results suggest that subvocal counting is impaired after anarthria.

Adult↗
PubMed1992

Inner speech in anarthria: neuropsychological evidence of differential effects of cerebral lesions on subvocal articulation.

The role of articulation in verbal short-term memory was investigated in two anarthric patients, C.M. and F.C., both showing normal comprehension for written and spoken language, above average intelligence and visuo-spatial abilities. Based on experimental results, we propose that subvocal articulation might be impaired in anarthric patients in different ways, according to the site of lesion: in 'locked-in' patients only the articulatory rehearsal processes necessary to enhance memory performances is involved, while in cortical anarthric patients the lesion affects the articulatory recoding processes involved in transferring visually presented material into an articulatory form for better retention.

Acoustic Stimulation↗
PubMed1991

Different patterns of dissociation in unilateral spatial neglect.

The aim of this paper is to discuss the issue of dissociations found in unilateral spatial neglect according to the modality of space exploration and the nature of the task. For this purpose we present a reanalysis of the data from a recent paper of Gentilini et al. (1989) comparing visual and blindfolded exploration of a computer keyboard and discuss the performance of a left-brain-damaged patient with right visuospatial neglect and left-sided neglect dyslexia. We conclude that unilateral spatial neglect cannot be interpreted as a disruption of a single attentional mechanism, but rather it reflects impaired attentional mechanisms at several levels of cognitive processing.

Adult↗