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Biomedical subjects

F Richer

Publications and source records attributed to F Richer.

At least 19 recordsLinked to original sources
PubMed2005

Sensorimotor mapping affects movement correction deficits in early Huntington's disease.

Huntington's disease (HD) is associated with early voluntary movement problems linked to striatal dysfunction. In pointing movements, HD increases the irregularity of the terminal part of movements, suggesting a dysfunction in error feedback control. We tested this hypothesis in movements requiring continuous feedback control. Patients in the early stages of HD and controls traced as fast and accurately as possible circles within a 5-mm annulus on a digitizing tablet when visual feedback of the hand and the circle was direct or indirect (through a monitor). Patients deviated more often from the annulus and showed larger corrections toward the circle than controls when using indirect visual feedback but not with direct visual feedback. When velocity requirements were removed, patients showed little change in these control problems. These results suggest that HD does not affect error feedback control in all movements and that the striatal contribution to voluntary movement is sensitive to sensorimotor mapping.

Adult↗
PubMed2004

Restless legs in Tourette syndrome.

Restless legs syndrome (RLS) and Tourette's syndrome (TS) share some common features, including the phenomenology of sensations relieved by movements, but few studies have examined the links between RLS and TS. We examined RLS and other TS comorbidities in 144 probands with TS or chronic tics and their parents. RLS was present in 10% of probands and 23% of parents with no gender differences. RLS in probands was linked significantly to maternal RLS but not paternal RLS, suggesting that a maternal RLS factor may contribute to the variable expression of TS.

Attention Deficit Disorder with Hyperactivity↗
PubMed2004

Tourette syndrome and dopaminergic genes: a family-based association study in the French Canadian founder population.

Tourette syndrome (TS) is a genetically complex disorder for which no causative genes have been unequivocally identified. Nevertheless, a number of molecular genetic studies have investigated several candidate genes, particularly those implicated in dopamine modulation. The results of these studies were inconclusive, which may be due, at least in part, to the variable ethnicity of the patients included in different studies and the chosen research design. In this study, we used a family-based association approach to investigate the implication of dopamine-related candidate genes, which had been previously reported as possibly associated with TS [genes that encode for the dopamine receptors DRD2, DRD3 and DRD4, the dopamine transporter 1 (SLC6A3) and the monoamine oxidase-A (MAO-A). The studied group was composed of 110 TS patients. These patients were selected from the French Canadian population, which displays a founder effect. Excess transmission of the 7-repeat allele of the DRD4 exon-3 VNTR polymorphism (chi(2) TDT =4.93, 1 df, P=0.026) and the putative 'high-activity' alleles of the MAO-A promoter VNTR polymorphism (chi(2) TDT =7.124, 1 df P=0.0076) were observed. These results were confirmed in a subgroup of patients with no attention deficit/hyperactivity or obsessive compulsive comorbid disorders. Haplotype analysis using one or two supplemental polymorphism in each of these genes confirmed these associations and allowed one to identify risk haplotypes. No associations were found for DRD2, DRD3 or SLC6A3. These data support the notion that DRD4 and MOA-A genes may confer an increased risk for developing TS in the French Canadian population.

Carrier Proteins↗
PubMed2000

Frontal brain lesions affect the use of advance information during response planning.

This study examined the nature of the response programming deficit after frontal cortex lesions through the effects of advance information on sequence initiation time. Nine patients with unilateral frontal lesions, 9 patients with temporal lesions, and 9 controls performed a sequential key-press task involving 4 rapid choice responses to a 4-letter stimulus. Three conditions manipulated the number of responses that subjects knew in advance. The frontal group showed slow initiation times in all conditions. Knowing the first response produced an acceleration of initiation time in all 3 groups. However, knowing 3 responses in advance instead of 1 further accelerated initiation time in the control and temporal groups but not in the frontal group. These results indicate that frontal lesions impair the use of multiple representations during programming. This suggests that the attentional control of response selection is an important element of the response planning deficit.

Adult↗
PubMed1999

Frontal lesions impair the attentional control of movements during motor learning.

This study examined the effects of frontal lobe lesions on the control of movements during motor learning. We compared the performance of patients with unilateral frontal or temporal excisions and controls in two-dimensional aiming movements during adaptation to a transformed visuomotor mapping. Subjects tried to reach a fixed target on a graphics tablet using indirect visual control from a monitor in either: (1) the standard visuomotor mapping, (2) a full inversion of motor space preserving the axis of movement, or (3) a mirror-like inversion of one axis of motor space. In the standard mapping, all groups showed precise and rapid aiming movements. In the full inversion condition, frontal lobe patients showed a stronger tendency than others to initiate movements in the natural direction (capture errors) during adaptation. In the mirror-like inversion, frontal patients showed deficits in both movement initiation and movement corrections. These control deficits disappeared with practice. These data provide evidence for a critical role of frontal cortex in the attentional control of unpracticed movements in man.

Adult↗
PubMed1999

Frontal cortex and the programming of repetitive tapping movements in man: lesion effects and functional neuroimaging.

Two studies examined the contribution of human frontal cortical areas to the programming of trains of repetitive movements. The first study compared the performance of patients with unilateral frontal excisions, unilateral temporal excisions and controls on the speed of initiation of discrete vs. sequential tapping movements to visual stimuli. The frontal group showed normal initiation times in single taps and a normal execution (pace and accuracy) in sequential taps but they were slower than the other groups at initiating sequential taps indicating a sequence programming problem for repetitions of a single response. A second study examined the functional anatomy of single and sequential taps in eight control subjects using fMRI. Subjects performed flexion/extension movements of the right thumb at either 1 movement/s or as trains of four closely spaced movements at a rate of 1 train/4 s. Statistical analyses revealed that primary sensorimotor cortex and a dorsolateral premotor cortex region were activated in both conditions. Medial frontal activation was not significant in discrete movements but was clearly present in sequential movements and involved SMA and cingulate regions bilaterally. In addition, two other dorsolateral premotor foci of activation were observed in the sequential taps condition. Results from these two experiments converge toward establishing a significant role of dorsolateral and medial premotor regions in the programming of trains of repetitive responses.

Adult↗
PubMed1996

Frontal lesions increase post-target interference in rapid stimulus streams.

We examined the effects of frontal lesions on the attentional processes surrounding the discrimination of target stimuli by comparing patients with frontal excisions, patients with temporal excisions and controls on target-letter identification in rapid visual streams. Subjects were asked to look at streams of 18-26 letters presented centrally at rates of 6, 8, or 10 letters/sec and to name the two white target letters (T1 and T2) embedded among black letters in each stream. The two target letters were separated by either 0, 2,4, or 6 black letters. Normals and temporals correctly reported T1 at all rates, they showed the expected T2 identification errors peaking 300 msec after T1 at high rate and little T2 interference at lower rates. However, frontals showed T2 interference at the two lower rates and were unable to identify T1 at high rate. The effects observed suggest that an inertia of target discrimination processes contributes to the frontal attention deficits.

Adult↗
PubMed1996

Inter-response interference contributes to the sequencing deficit in frontal lobe lesions.

In this study we investigated the contribution of inter-response interference to the sequencing deficit in frontal lobe lesions. We examined inter-response interference in choice sequences through the reduction in inter-response interval produced by stimulus preview when compared with sequences performed without preview. If frontal lobe lesions result in a stronger inter-response interference, the facilitative effect of preview on inter-response interval should be attenuated. We compared nine patients with a frontal excision with nine patients with a temporal excision and nine controls in a task requiring rapid keypress responses to each of five letters in a sequence. In the no-preview condition, the five letters were presented one at a time, immediately following the previous response. In the preview condition, the five letters were presented simultaneously before the response sequence. Patients with a frontal lesion showed slower response times than the other groups. In normal subjects and patients with a temporal lesion, stimulus preview produced the expected reduction of inter-response time and the slowing of sequence initiation. In frontal lesions, however, preview did not reduce inter-response time and exacerbated the slowing of sequence initiation. The results indicate that patients with a frontal lobe lesion show increased interference between adjacent responses as well as a sequence initiation problem.

Adult↗
PubMed1996

Outcome of severe congenital hypothyroidism: closing the developmental gap with early high dose levothyroxine treatment.

We have previously reported that despite neonatal screening, children with severe congenital hypothyroidism treated at 5 weeks of age with 6 micrograms/kg.day levothyroxine have clinically significant intellectual impairment, whereas those with the moderate form of the disease are indistinguishable from controls. The developmental outcome of children with severe congenital hypothyroidism treated earlier with higher initial doses of levothyroxine remained to be determined. In the present study, 45 infants with permanent congenital hypothyroidism detected by neonatal screening are described. For the group, the median age at starting treatment was 14 days, and the median initial dose of levothyroxine was 11.6 micrograms/kg.day. Based on the area of their knee epiphyses at diagnosis, the patients were divided into 2 subgroups: severe (< 0.05 cm2; n = 10) and moderate (> or = 0.05 cm2; n = 35). The psychomotor development of 8 patients in each subgroup, matched for the socioeducational level of their families, was assessed at 18 months. Mean plasma free T4 levels were supraphysiological during the first few months of life, but mean plasma T3 levels remained within the normal range, and there were no signs or symptoms of hyperthyroidism. The mean plasma TSH concentration was less than 4.5 mIU/L 4 weeks after starting treatment. Bone maturation remained delayed at 12 months in the severe cases and was not unduly advanced in the moderate cases. The mean (+/- SD) developmental quotients at 18 months were similar in severe and moderate cases (107 +/- 10 and 110 +/- 5, respectively). We conclude that with earlier treatment and a higher initial dose of levothyroxine, the early developmental outcome of infants with severe congenital hypothyroidism is now indistinguishable from that of infants with the moderate form of the disease who were used as controls.

Child Development↗
PubMed1995

Response selection deficits in frontal excisions.

We compared the performance of patients with frontal excisions, patients with temporal excisions and controls in tasks involving speeded choice responses in which a number of variables were manipulated including: perceptual difficulty, stimulus and response set-size, associative complexity, and spatial stimulus-response compatibility. Response times were sensitive to all manipulations but did not show any group differences. The error rates of the three groups were equally affected by perceptual difficulty and response set-size but frontals were preferentially affected by spatial S-R compatibility, associative complexity, and the number of stimuli per response. The results are consistent with a basic deficit in response selection processes which could underly many problems produced by frontal lesions.

Adult↗
PubMed1993

Target detection deficits in frontal lobectomy.

We examined the hypothesis of dorsomedial frontal lobe involvement in target detection through the effects of distractor interference and multiple target interference on unilateral lobectomy patients. Seven patients who underwent a unilateral frontal lobectomy for epilepsy involving dorsomedial cortex and variable amounts of lateral cortex were compared to 10 patients with a unilateral temporal lobectomy and to 10 normal adults on a visual character cancellation task. The task involved detecting occurrences of target characters embedded in rows of characters under three conditions: detection of one target character in the absence of distractors, detection of one target character among distractors, and detection of three targets among distractors. Visual detection performance was compared to that in the Stroop reading interference task. Frontals were predictably slower than the other groups in the baseline conditions of the character cancellation task and the Stroop task. After partialing out baseline detection performance in the character cancellation task, frontals showed an almost normal detection in the presence of distractors but were distinctly slower and made more errors than the other groups in multiple target detection. Frontals were also slower on the Stroop even after partialing out baseline naming performance. Temporals were normal on all tasks. Results suggest that frontal damage can affect selectivity in target detection as well as the Stroop and that this deficit is independent of the general psychomotor slowing observed in these patients.

Adolescent↗
PubMed1993

Stimulation of human somatosensory cortex: tactile and body displacement perceptions in medial regions.

We examined the somatosensory perceptions evoked by stimulation of rolandic and parietal brain regions in 40 epileptic patients undergoing a presurgical investigation with intracerebral electrodes. Bipolar stimulation trains were delivered in an incremental sequence at medial and/or lateral contact pairs of stereotaxically implanted, multi-contact electrodes, while monitoring stimulus after discharge propagation with electrodes in frontal and temporal lobes. Rolandic stimulation evoked contralateral sensations, whereas sensations from either side were evoked in the opercular region. Stimulation of lateral posterior parietal cortex evoked only few sensations and these were restricted to the supramarginal gyrus. Contralateral sensations were evoked in the posterior cingulate gyrus, whereas ipsilateral sensations were evoked in the vicinity of the cingulate sulcus. Complex proprioceptive sensations in the form of bilateral feelings of levitation were elicited in a medial parietal region around the subparietal sulcus and not at any other site. These perceptions were not accompanied by any movement, tactile, or vestibular sensations, suggesting that the human sub-parietal sulcus region is linked to the proprioceptive processing system.

Electrodes↗
PubMed1993

Persistent neuropsychological deficits and vigilance impairment in sleep apnea syndrome after treatment with continuous positive airways pressure (CPAP).

The obstructive sleep apnea syndrome is characterized by nocturnal sleep disturbance, excessive daytime sleepiness and neuropsychological deficits in the areas of memory, attention, and executive tasks. In the present study, these clinical manifestations were assessed in apneic patients before and 6 months after treatment with nasally applied continuous positive airway pressure (CPAP). CPAP treatment was found to restore normal respiration during sleep and to normalize sleep organization. Daytime vigilance greatly improved with treatment but some degree of somnolence as compared to normal controls persisted. Similarly, most neuropsychological deficits normalized with treatment. The exception was for planning abilities and manual dexterity, two neuropsychological deficits that have been found to be highly correlated with the severity of nocturnal hypoxemia. These results raise the possibility that anoxic brain damage is a pathogenic factor in severe obstructive sleep apnea syndrome.

Adult↗
PubMed1993

Perceptual context and the selective attention effect on auditory event-related brain potentials.

Two experiments examined the effect of the perceptual context established through tonal grouping on neuroelectric responses during selective listening. Subjects monitored one of the extreme pitches in four-pitch tone sequences and detected rare longer tones of the designated pitch. In the first study, tonal grouping was manipulated by changing the tonal separation between the extreme pitches and their nearest neighbor, keeping the extreme pitches constant. Grouping increased the negativity of the attended-unattended difference potential. A second study examined the effect of grouping on the attention-related negativity when it opposed the effect of physical similarity. The proximity of extreme pitches varied, keeping the middle pitches constant. The effect of grouping on event-related potentials (ERPs) for the middle pitches was varied according to the tone being attended. ERPs for the middle tone adjacent to the attended tone became more negative with grouping, whereas ERPs for the distant middle tone became less negative with grouping. These effects suggest that the attention-related negativity is sensitive to contextual information.

Adult↗
PubMed1992

Neurobehavioral manifestations in obstructive sleep apnea syndrome before and after treatment with continuous positive airway pressure.

Obstructive sleep apnea syndrome (OSAS) is characterized by recurrent apneas during sleep, resulting in repetitive hypoxemic episodes and a constant interruption of the normal sleep pattern. Vigilance impairment and neuropsychological deficits are among the main symptoms seen in this condition. One of the major questions in this field concerns the reciprocal interactions between nocturnal hypoxemia, sleep disruption, excessive daytime sleepiness and cognitive deficits. Results of this study suggest that vigilance impairment is attributable mostly to nocturnal hypoxemia. However, in cognitive deficits, hypoxemia seems to play a major role in executive and psychomotor tasks, whereas attention and memory functions appear to be related to vigilance impairment. After treatment, hypoxemia-related deficits and some degree of sleepiness persist. These results raise the possibility of an irreversible anoxic central nervous system (CNS) damage in severe OSAS.

Adult↗
PubMed1992

[Research and surgical treatment of epilepsy].

The currently available surgical procedures for the treatment of epilepsy, from fundamental data to therapeutic results, including various means of investigation are reported. The work is based on a review of the literature and on the cases studied by the two teams from the Universities of Montreal and Bordeaux who share the same concept of epilepsy surgery. The patient groups of the two teams include 316 S.E.E.G., 214 cortectomies, 39 callosotomies and 2 multiple sub-pial transsections. In the first part, the authors attempt to demonstrate that the epileptic focus corresponds to the region where the seizures arise, that this focus is not directly comparable to the region where inter-ictal spikes are recorded and sometimes becomes autonomous from the causal lesion. The epileptic phenomenon has a definite harmful effect on cerebral functions and a probable self-aggravating potential. The second chapter summarizes the clinical data on which the indications and contraindications are based. These obviously depend on whether the intervention is intended to be curative or palliative. Various non-invasive and invasive investigations are then reviewed, according to their relative importance and the experience of each team. The main points developed are: the electroclinical correlations during seizures, the symptomatological data for differentiating between temporal and frontal lobe seizures, the contribution of M.R.I. in demonstrating the epileptogenic and epileptic lesions, the electrophysiological information suggesting that S.E.E.G. remains the most informative mean of investigation. The various methods of investigation of assessing electrical, functional (cerebral blood flow, metabolism) and morphological aspects of epilepsy, supply non-redondant findings about the localisation of the epileptic focus. The chapter on surgical techniques mainly discusses the various modes of implantation of subdural and intracerebral electrodes and reports the same rate of morbidity in both cases. Orthogonal teleradiography is still perfectly suited to the implantation of intracerebral electrodes. S.E.E.G. is still the most anatomically precise technique. However, in certain conditions, extraoperative E.Co.G. is more adequate. New surgical modalities have recently appeared such as the multiple subpial transsections which allow treatment of epileptic foci unapproachable by cortectomy and such as modified techniques of hemispherectomy, which by decreasing morbidity, renew interest in them. In the chapter on surgical results, the authors emphasize the methodological problems of evaluation that partly account for their wide variability. The results obtained with the various surgical modalities are reviewed. The outcome in cortectomies is discussed at length in terms of the data from the literature as well as the results reported by both teams.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗