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Biomedical subjects

M Lassonde

Publications and source records attributed to M Lassonde.

At least 19 recordsLinked to original sources
PubMed2006

Cross-modal reorganization and speech perception in cochlear implant users.

Recent work suggests that once the auditory cortex of deaf persons has been reorganized by cross-modal plasticity, it can no longer respond to signals from a cochlear implant (CI) installed subsequently. To further examine this issue, we compared the evoked potentials involved in the processing of visual stimuli between CI users and hearing controls. The stimuli were concentric circles replaced by a different overlapping shape, inducing a shape transformation, known to activate the ventral visual pathway in human adults. All CI users had their device implanted for >1 year, but obtained different levels of auditory performance following training to establish language comprehension. Seven of the 13 patients showed good capacities for speech recognition with the CI (good performers) while the six others demonstrated poor speech recognition abilities (poor performers). The evoked potentials of all patients showed larger amplitudes, with different distributions of scalp activations between the two groups. The poor performers exhibited broader, anteriorly distributed, high P2 amplitudes over the cortex whereas the good performers showed significantly higher P2 amplitudes over visual occipital areas. These results suggest the existence of a profound cross-modal reorganization in the poor performers and an intramodal reorganization in the good performers. We interpret these data on the basis of enhanced audiovisual coupling as the key to a long-term functional improvement in speech discrimination in CI users.

Adolescent↗
PubMed2006

The effect of visors on head and facial injury in National Hockey League players.

There has been an increase in the number of concussions sustained by players in the National Hockey League (NHL). While wearing a helmet is now required by the NHL, the face visor remains optional. It is unknown to what degree face visors influence concussion, other head injury and eye-injury rates at the professional level. Data from the 2001-2002 NHL season were examined. It was found that wearing a face visor did not significantly influence the prevalence of concussion. Visor protection did, however, minimise eye-injuries and other, non-concussion head injuries. These data suggest that, while a visor may prevent some head and eye-injuries, other measures may be necessary to reduce the number of concussions.

Craniocerebral Trauma↗
PubMed2006

Electrophysiological markers of visuocortical development.

The development of noninvasive techniques for the assessment of functional brain maturation is critical. The present study analyzed 63 babies' and children's (27 days to 5.5 years) cerebral responses to a pattern-reversal visual stimulation using high-density (128 electrodes) electrophysiological recordings. Developmental data were further compared with those of young adults (n = 16). Tremendous changes in pattern visual evoked potentials (pVEPs) morphology were observed between 7 and 24 months characterized by the emergence of negative components labeled "N70" and "N145" and the reduction of the P100 amplitude. The adult pattern of response appears from 24 months onward. Spectral density values show an increase of higher frequencies with age. Coherence values show a reduction between 3 and 23 months of age as well as a further increase toward adulthood between areas implicated in visual processing. These results are discussed in light of developmental features such as synaptogenesis, myelination, and neuronal networks refinement.

Adult↗
PubMed2005

Interaction between the flash evoked SSVEPs and the spontaneous EEG activity in children and adults.

OBJECTIVE: To evaluate the interaction between the steady-state visual evoked potentials (SSVEPs) recorded during the intermittent photic stimulation (IPS) and the spontaneous EEG activities both in children and adults. METHODS: EEG was recorded during the rest and under 5, 7.5, 10 and 12.5 Hz IPS in 41 children between 3 and 16 years and 10 adults. We distinguished between the spontaneous resting EEG spectra, SSVEPs (1st harmonic) and undriven (ongoing) EEG spectra recorded during the IPS. RESULTS: We show that IPS influences spontaneous EEG activity by specifically suppressing or desynchronizing individual posterior dominant resting EEG frequencies (DF) in both children and adults. Further, this highly significant and consistent suppressing effect positively correlates with the SSVEPs amplitude. CONCLUSIONS: Our data suggest that the desynchronization of the spontaneous EEG activity under IPS and the SSVEPs are related to each other. SIGNIFICANCE: These relationships could be interesting to study in pathological conditions where the neural synchronization and the responses to IPS have been shown to be affected, such as epilepsy and schizophrenia.

Adolescent↗
PubMed2005

Impact of childhood epilepsy on reading and phonological processing abilities.

Although children with epilepsy tend to exhibit more reading difficulties than their classmates, no systematic studies have investigated the relationship between these difficulties and epilepsy. As functional neuroimaging studies have implicated both temporal and frontal lobes in the phonological aspect of reading [K.R. Pugh, B.A. Shaywitz, S.E. Shaywitz, et al. Brain 1996;119:1221-38], seizure activity originating in either region could interfere with phonological processing, whereas generalized seizures would not disturb this function as much. To explore this hypothesis, we compared the metaphonological skills of school-aged children with either temporal lobe epilepsy (TLE), frontal lobe epilepsy (FLE), or generalized absence seizures (ABS) with those of healthy controls. While the reading ability of all epileptic children was close to 2 years behind expectations, children with TLE did not differ from the controls on phonological tasks. In contrast, children with FLE exhibited significant deficits, whereas children with ABS showed difficulties restricted to phonemic segmentation. The results suggest that FLE and, to a lesser extent, generalized seizures may interfere with phonological processing, whereas TLE may affect other aspects of reading.

Analysis of Variance↗
PubMed2004

Blind subjects process auditory spectral cues more efficiently than sighted individuals.

The goal of the present study was to investigate how monaural sound localization on the horizontal plane in blind humans is affected by manipulating spectral cues. As reported in a previous study (Lessard et al. 1998), blind subjects are able to calibrate their auditory space despite their congenital lack of vision. Moreover, the performance level of half of the blind subjects was superior to that of sighted subjects under monaural listening conditions. Here, we first tested ten blind subjects and five controls in free-field (1) binaural and (2) monaural sound localization tasks. Results showed that, contrary to controls and half the blind subjects, five of the blind listeners were able to localize the sounds with one ear blocked. The blind subjects who showed good monaural localization performances were then re-tested in three additional monaural tasks, but we manipulated their ability to use spectral cues to carry out their discrimination. These subjects thus localized these same sounds: (3) with acoustical paste on the pinna, (4) with high-pass sounds and unobstructed pinna and (5) with low-pass sounds and unobstructed pinna. A significant increase in localization errors was observed when their ability to use spectral cues was altered. We conclude that one of the reasons why some blind subjects show supra-normal performances might be that they more effectively utilize auditory spectral cues.

Acoustic Stimulation↗
PubMed2004

[Neuropsychological profile of intractable partial epilepsies].

The neuropsychological assessment is an essential part of the clinical work-up of patients suffering from pharmaco-resistant epilepsy. The aim of the present article is to give an overview of the assessment with regard to the functions tested, the techniques employed and the factors influencing the interpretation of the results. In the first part of the article, the role of the neuropsychological evaluation is discussed in relation to other methods of clinical investigation, such as EEG, brain imaging techniques and sodium amytal exploration, all of which intend to identify the localization (region and laterality) of the epileptogenic focus. This is particularly important for patients slated for epilepsy surgery. In addition, the neuropsychological exam aims to determine the extent of the deficits in various cognitive and sensori-motor domains by taking into account the structural and/or functional reorganization that may have taken place and the compensatory mechanisms that are available to the patient. In this context, the effect of various factors influencing the mental and emotional functioning of the patient, such as the age at onset and duration of the epilepsy, the presence of a structural lesion, the type and number of anticonvulsant drugs, the personality and the adaptability of the patient must be considered. In children, the effect of recurrent seizures may be more devastating since these risk to interfere with normal brain development. On the other hand, the greater plasticity of the immature brain provides a larger window in which compensation can take place. Evidence suggests that attentional processes are affected in all types of epilepsy. Furthermore, the antiepileptic medication may have a deleterious effect on the cognitive and emotional status of the patient, particularly in patients with pharmaco-resistant epilepsy who are usually taking a combination of anticonvulsant drugs. The second part of the article presents localization-specific neuropsychological impairments and the tests most suited to reveal these deficits. Thus, in temporal lobe epilepsy, memory functions are more affected than in other types of partial epilepsy, whereas intellectual functions are usually preserved. However, recent studies cast some doubt on the prevailing view that left-hemisphere foci are associated with verbal memory deficits only and that right-hemisphere foci solely affect visuo-spatial memory. The dichotomy appears to be more subtle, especially in patients with a long-standing seizure history. Frontal foci produce deficits in motor coordination, attention, working memory and executive functions. These deficits appear to be more pronounced in children than in adults. Few studies have explored the neuropsychological consequences of parieto-occipital foci given that this type of epilepsy is relatively rare. The neuropsychological profile of the patient should guide healthcare providers to implement the necessary remedial measures to facilitate the patient's social integration and to improve his quality of life.

Adult↗
PubMed2003

Impact of temporal lobe epilepsy on phonological processing and reading: a case study of identical twins.

In order to evaluate the possible consequences of temporal lobe epilepsy on reading acquisition, we first compared the reading skills and phonological awareness abilities in a set of 13-year-old identical twins, one of whom is affected by temporal lobe epilepsy (LB). We then compared their performances to those of an age- and IQ-matched control group. Both siblings have an intellectual quotient above average as well as normal memory and linguistic abilities. Results showed that the reading age of LB (assessed by the Lefabvrais French reading test) was more than two years behind expectations whereas that of her sister was above average. Further, in contrast to her sister and healthy control subjects, LB exhibited specific deficits in elaborate metaphonological awareness abilities (non-word repetition, rhyme production, phonemic segmentation and syllabic inversion). These could be linked to temporal lobe dysfunction, thus confirming the important role of the temporal lobes in reading acquisition.

Adolescent↗
PubMed2001

Hyperbaric oxygen for children with cerebral palsy: a randomised multicentre trial. HBO-CP Research Group.

BACKGROUND: The use of hyperbaric oxygen for children with cerebral palsy has spread worldwide, despite little scientific evidence of efficacy. We did a randomised trial to assess the efficacy and side-effects of this form of therapy in children with cerebral palsy. METHODS: 111 children with cerebral palsy aged 3-12 years were randomly assigned hyperbaric oxygen (n=57) or slightly pressurised room air (n=54). All children received 40 treatments over 2 months. Hyperbaric oxygen treatment was 1 h in 100% oxygen at 1.75 atmospheres absolute (ATA); children on slightly pressurised air received air at 1.3 ATA (the lowest pressure at which pressure can be felt, thereby ensuring the maintenance of masking). The main outcome measure was gross motor function. Secondary outcomes included performance in activities of daily living, attention, working memory, and speech. FINDINGS: For all outcomes, both groups improved over the course of the study, but without any difference between the two treatments. The score on the global gross motor function measure increased by 3.0% in the children on slightly pressurised air and 2.9% in those on hyperbaric oxygen. The mean difference between treatments was -0.40 (95% CI -1.69 to 0.90, p=0.544). Other changes were seen in speech, attention, memory, and functional skills. Ear problems occurred in 27 children treated by hyperbaric oxygen and in 15 treated with hyperbaric air (p=0.004). INTERPRETATION: In this study, hyperbaric oxygen did not improve the condition of children with cerebral palsy compared with slightly pressurised air. The improvement seen in both groups for all dimensions tested deserves further consideration.

Cerebral Palsy↗
PubMed2001

Callosal contribution to procedural learning in children.

A previous study in acallosal patients (De Guise, et al., 1999) has demonstrated the crucial role of the corpus callosum (CC) in a procedural learning task that requires the participation of both hemispheres. Because children often display limitations in interhemispheric communication linked to callosal immaturity, we expected that they would have difficulties learning a procedural skill that involved interhemispheric integration during its acquisition, but not when the skill was learned intrahemispherically. To test this hypothesis, 40 children, divided into 4 age groups (6 to 8 years, 9 to 11 years, 12 to 14 years, and 15 to 16 years), performed a modified version of the serial reaction time task developed by Nissen and Bullemer (1987). This task involves uni- or bimanual key-pressing responses to a fixed sequence of 10 visual stimuli that are repeated 80 times. All the children were able to learn the visuomotor skill in the unimanual condition and to transfer it interhemispherically. However, only the older children (12 years and over) learned the task in the bimanual (interhemispheric) condition. The results indicate that the maturation of the CC affects interhemispheric acquisition of a procedural skill in two different ways: While the immature CC appears to be sufficient to transfer a skill acquired by one hemisphere, a mature CC seems to be required to learn the skill bihemispherically. The latter skill was achieved around the age of 12, coinciding with the end of the maturation cycle of the CC. Although the young children were unable to learn the bimanual task implicitly, some of them showed explicit knowledge of the procedure, confirming once again the dissociation between explicit and implicit memory suggested by Squire (1992).

Adolescent↗
PubMed2001

Recommendations for grading of concussion in athletes.

Mild sports-related concussions, in which there is no loss of consciousness, account for >75% of all sports-related brain injury. Universal agreement on concussion definition and severity grading does not exist. Grading systems represent expertise of clinicians and researchers yet scientific evidence is lacking. Most used loss of consciousness and post-traumatic amnesia as markers for grading concussion. Although in severe head injury these parameters may have been proven important for prognosis, no study has done the same for sport-related concussion. Post-concussion symptoms are often the main features to help in the diagnosis of concussion in sport. Neuropsychological testing is meant to help physicians and health professionals to have objective indices of some of the neurocognitive symptoms. It is the challenge of physicians, therapists and coaches involved in the care of athletes to know the symptoms of concussion, recognise them when they occur and apply basic neuropsychological testing to help detect this injury. It is, therefore, recommended to be familiar with one grading system and use it consistently, even though it may not be scientifically validated. Then good clinical judgement and the ability to recognise post-concussion signs and symptoms will assure that an athlete never returns to play while symptomatic.

Athletic Injuries↗
PubMed2000

Concussions in athletes produce brain dysfunction as revealed by event-related potentials.

We have used event-related potentials (ERP) to assess cerebral activity following mild traumatic brain injuries in 20 college athletes practising contact sports. Concussion victims showed a striking decrease in P300 amplitude, an effect presumed to reflect alterations in attentional-cognitive processes. Moreover, the degree of impairment was strongly related to the severity of post-concussion symptoms. Our data suggest that concussions cause objectively measurable changes in the electrophysiological markers of brain activity and hence in the functions of the structures from which they originate. ERPs may thus constitute a reliable method to accurately monitor the clinical course and recovery of head injuries in athletes.

Adult↗
PubMed2000

Sensorimotor organization in patients who have undergone hemispherectomy: a study with (15)O-water PET and somatosensory evoked potentials.

To identify cortical structures that subserve residual motor and sensory function in patients with congenital hemiparesis due to a porencephalic cyst, we examined, using [(15)O]H2O, PET and somatosensory evoked potentials (SEPs) in three patients with left-sided hemiparesis who had undergone hemispherectomy. Motor stimulation of the affected hand produced ipsilateral activation in the premotor area in all patients, the SMA in two patients, and SII in two patients. Vibrotactile stimulation resulted in activation of the ipsilateral SII in all subjects. Median nerve stimulation of the affected hand produced ipsilateral long-latency SEPs in fronto-centro-parietal areas, whereas stimulation of the non-affected hand produced normal early cortical potentials in the contralateral hemisphere. Our results suggest that residual function in the paretic hand is warranted through non-primary motor and sensory areas, and higher order associative areas in the intact hemisphere.

Adult↗
PubMed2000

An fMRI study of the lateralization of motor cortex activation in acallosal patients.

Transcranial magnetic stimulation (TMS) studies have suggested that callosal afferents may mediate inhibition of the ipsilateral motor cortex (IMC) during unilateral hand movements. To test this concept, we used fMRI to determine whether acallosal patients have increased IMC activation with either complex or simple unilateral finger movements. Neither the localization of motor cortical regions activated, the volumes of activation, or the relative hemispheric lateralization of activations were different between the patients and normal controls. The potential callosal inhibitory pathway identified by TMS therefore does not appear to contribute to the interhemispheric suppression of physiologically relevant activations in the motor cortex as measured by fMRI.

Adult↗
PubMed2000

Brain functional reorganization in early blind humans revealed by auditory event-related potentials.

Visually challenged individuals often compensate for their handicap by developing supra-normal abilities in their remaining sensory systems. Here, we examined the scalp distribution of components N1 and P3 of auditory evoked potentials during a sound localization task in four totally blind subjects who had previously shown better performance than sighted subjects. Both N1 and P3 waves peaked at their usual positions while blind and sighted individuals performed the task. However, in blind subjects these two components were also found to be robust over occipital regions while in sighted individuals this pattern was not seen. We conclude that deafferented posterior visual areas in blind individuals are recruited to carry out auditory functions, enabling these individuals to compensate for their lack of vision.

Acoustic Stimulation↗
PubMed2000

Sound localization in hemispherectomized subjects: the contribution of crossed and uncrossed cortical afferents.

The aim of the present study was to evaluate how hemispherectomized subjects localize sounds in free field using residual auditory structures under monaural testing conditions. The main objective of using a monaural condition with these subjects, who lack the terminal fields of auditory projections on one side, was to evaluate how the crossed and uncrossed pathways compare, with the aim of resolving this biologically critical function. In this model, crossed and uncrossed inputs refer to auditory stimulation presented to the unobstructed ear on the contralateral and the ipsilateral side of the intact hemisphere, respectively. Three hemispherectomized subjects (Hs) and ten control subjects (Cs) were tested for their accuracy to localize broad band noise bursts (BBNBs) of fixed intensity presented on the horizontal plane. BBNBs were delivered randomly through 16 loudspeakers mounted at 10 degrees intervals on a calibrated perimeter frame located inside an anechoic chamber. Subjects had to report the apparent stimulus location by pointing to its perceived position on the perimeter. Hs were less accurate than Cs in the baseline binaural condition, confirming the finding that with a single hemisphere and/or residual (subcortical) structures they cannot analyze binaural cues to sound localization as efficiently as with two fully functional hemispheres. In the monaural condition, Hs localized poorly when they had to depend on the uncrossed input, but performed as well or even better than the Cs with the crossed input. These findings suggest that monaural spectral cues, which constitute the only residual cue to localization under the monaural testing condition, are treated more efficiently, that is, they lead to better localization performance when relayed to the cortex via crossed pathways than through uncrossed pathways.

Adolescent↗