Biomedical subjects

Anne-Lise Giraud

Publications and source records attributed to Anne-Lise Giraud.

9 recordsLinked to original sources

PubMed2006

Cortical activity at rest predicts cochlear implantation outcome.

The functional status of central neural pathways, in particular their susceptibility to plasticity and functional reorganization, may influence speech performance of deaf cochlear implant users. In this paper, we sought to determine how brain metabolic activity measured before implantation relates to cochlear implantation outcome, that is, speech perception. In 22 prelingually deaf children between 1 and 11 years, we correlated preoperative glucose metabolism as measured by F-18 fluorodeoxyglucose positron emission tomography with individual speech perception performance assessed 3 years after implantation, while factoring out the confounding effect of age at implantation. Whereas age at implantation was positively correlated with increased activity in the right superior temporal gyrus, speech scores were selectively associated with enhanced metabolic activity in the left prefrontal cortex and decreased metabolic activity in right Heschl's gyrus and in the posterior superior temporal sulcus. These results reinforce the notion that implantation should be performed as early as possible to prevent cross-modal takeover of auditory regions and suggest that rehabilitation strategies may be more efficient if they capitalize on general cognitive functions instead of only targeting specialized circuits dedicated to auditory and audiovisual pattern recognition.

Auditory Cortex↗

PubMed2006

Implicit multisensory associations influence voice recognition.

Natural objects provide partially redundant information to the brain through different sensory modalities. For example, voices and faces both give information about the speech content, age, and gender of a person. Thanks to this redundancy, multimodal recognition is fast, robust, and automatic. In unimodal perception, however, only part of the information about an object is available. Here, we addressed whether, even under conditions of unimodal sensory input, crossmodal neural circuits that have been shaped by previous associative learning become activated and underpin a performance benefit. We measured brain activity with functional magnetic resonance imaging before, while, and after participants learned to associate either sensory redundant stimuli, i.e. voices and faces, or arbitrary multimodal combinations, i.e. voices and written names, ring tones, and cell phones or brand names of these cell phones. After learning, participants were better at recognizing unimodal auditory voices that had been paired with faces than those paired with written names, and association of voices with faces resulted in an increased functional coupling between voice and face areas. No such effects were observed for ring tones that had been paired with cell phones or names. These findings demonstrate that brief exposure to ecologically valid and sensory redundant stimulus pairs, such as voices and faces, induces specific multisensory associations. Consistent with predictive coding theories, associative representations become thereafter available for unimodal perception and facilitate object recognition. These data suggest that for natural objects effective predictive signals can be generated across sensory systems and proceed by optimization of functional connectivity between specialized cortical sensory modules.

Acoustic Stimulation↗

PubMed2005

Voice recognition and cross-modal responses to familiar speakers' voices in prosopagnosia.

Recognizing the voices of people we know does not only activate "voice areas" in the temporal lobe but also extraauditory areas including the fusiform "face area" (FFA). This cross-modal effect could reflect that individual face and voice information become specifically associated when becoming acquainted with a person. Here, we addressed whether the ability to have individual face representations 1) plays a role in voice recognition and 2) is required to observe cross-modal responses to voices in face areas. We compared speaker recognition performance and neuroimaging responses during the processing of familiar and nonfamiliar speakers' voices in a developmental prosopagnosic subject (SO) with the respective findings obtained in a group of 9 control subjects. Despite scoring worse than controls on recognition of familiar speakers' voices, SO had normal cross-modal responses in the FFA and normal connectivity between FFA and the voice regions. However, she had reduced activations in areas that usually respond to familiarity with people. An indication for the malfunctioning of her FFA was reduced connectivity of the FFA to a subset of these supramodal areas. In combination these data suggest that 1) voice recognition benefits from the ability to process faces at an individual level and 2) cross-modal association of voices and faces in the brain is achieved by a sensory binding and does not depend on a top-down mechanism subsequent to successful person recognition.

Acoustic Stimulation↗

PubMed2005

Cortical plasticity associated with stuttering therapy.

UNLABELLED: Neuroimaging studies have indicated that persistent developmental stuttering (PDS) may be associated both with an abnormality in white matter of left-hemispheric speech areas and a right-hemispheric hyperactivity. The latter may compensate for the deficient structural connectivity in the left hemisphere. To investigate the effects of stuttering therapy on brain activity nine male adults with PDS underwent functional magnetic resonance imaging (fMRI) before and within 12 weeks after fluency shaping therapy. Brain response differences during overt sentence reading before and after therapy were assessed by utilizing random effects analyses. After therapy, a more widespread activation was observed in frontal speech and language regions and temporal areas of both hemispheres, particularly and more pronounced on the left side. Interestingly, distinct posttreatment left-sided activation increases were located directly adjacent to a recently detected area of white matter anomaly [M. Sommer, M.A. Koch, W. Paulus, C. Weiller, C. Buchel (2002). Disconnection of speech-relevant brain areas in persistent developmental stuttering. The Lancet, 360, 380-383] suggesting that fluency shaping techniques reorganize neuronal communication between left-sided speech motor planning, motor execution, and temporal areas. Hence, a therapeutic mechanism can be assumed to remodel brain circuitry close to the source of the dysfunction instead of reinforcing compensation via homologous contralateral brain networks. EDUCATIONAL OBJECTIVES: The reader will learn about and be able to: (1) describe brain activation changes detected shortly after fluency-shaping therapy; (2) identify left-hemispheric regions where a (re)functionalization after fluency-shaping therapy seems to occur adjacent to a recently described abnormal white matter region in PDS subjects; and (3) discuss how an effective cerebral compensation mechanism for stuttering could work.

Adult↗

PubMed2005

Interaction of face and voice areas during speaker recognition.

Face and voice processing contribute to person recognition, but it remains unclear how the segregated specialized cortical modules interact. Using functional neuroimaging, we observed cross-modal responses to voices of familiar persons in the fusiform face area, as localized separately using visual stimuli. Voices of familiar persons only activated the face area during a task that emphasized speaker recognition over recognition of verbal content. Analyses of functional connectivity between cortical territories show that the fusiform face region is coupled with the superior temporal sulcus voice region during familiar speaker recognition, but not with any of the other cortical regions normally active in person recognition or in other tasks involving voices. These findings are relevant for models of the cognitive processes and neural circuitry involved in speaker recognition. They reveal that in the context of speaker recognition, the assessment of person familiarity does not necessarily engage supramodal cortical substrates but can result from the direct sharing of information between auditory voice and visual face regions.

Acoustic Stimulation↗

PubMed2004

Distinct functional substrates along the right superior temporal sulcus for the processing of voices.

The right superior temporal sulcus (STS) is involved in processing the human voice. In this paper, we report fMRI findings showing that segregated cortical regions along the STS are involved in distinct aspects of voice processing and that they functionally cooperate during speaker recognition. Subjects listened to identical sets of auditory sentences while recognizing either a target sentence irrespective of the speaking voice or a target voice irrespective of the sentence meaning. As the same stimulus material was used in both conditions, task-related activations were not confounded by differences in speech acoustic features. Half of the stimuli were voices of familiar persons and half of persons that were never encountered before. Recognizing voices activated the right anterior and posterior STS more than recognizing verbal content. While the right anterior STS responded equally to both voice categories, the right posterior STS displayed stronger responses to non-familiar than to familiar speakers' voices. It also responded to our baseline condition of amplitude modulated noises that required a detailed analysis of complex temporal patterns. Analyses of connectivity (psychophysiological interactions) revealed that during speaker recognition both anterior and posterior right STS interacted with a region in the mid/anterior part of the right STS, a region that has been implicated in processing the acoustic properties of voices. Moreover, the anterior and posterior STS displayed distinct connectivity patterns depending on familiarity. Our results thus distinguish three STS regions that process different properties of voices and interact in a specific manner depending on familiarity with the speaker.

Acoustic Stimulation↗

PubMed2003

A supramodal number representation in human intraparietal cortex.

The triple-code theory of numerical processing postulates an abstract-semantic "number sense." Neuropsychology points to intraparietal cortex as a potential substrate, but previous functional neuroimaging studies did not dissociate the representation of numerical magnitude from task-driven effects on intraparietal activation. In an event-related fMRI study, we presented numbers, letters, and colors in the visual and auditory modality, asking subjects to respond to target items within each category. In the absence of explicit magnitude processing, numbers compared with letters and colors across modalities activated a bilateral region in the horizontal intraparietal sulcus. This stimulus-driven number-specific intraparietal response supports the idea of a supramodal number representation that is automatically accessed by presentation of numbers and may code magnitude information.

Acoustic Stimulation↗

PubMed2003

The nature and treatment of stuttering as revealed by fMRI A within- and between-group comparison.

UNLABELLED: This article reviews some of our recent functional magnetic resonance imaging (fMRI) studies of stuttering. Using event-related fMRI experiments, we investigated brain activation during speech production. Results of three studies comparing persons who stutter (PWS) and persons who do not stutter (PWNS) are outlined. Their findings point to a region in the right frontal operculum (RFO) that was consistently implicated in stuttering. During overt reading and before fluency shaping therapy, PWS showed higher and more distributed neuronal activation than PWNS. Immediately after therapy differential activations were even more distributed and left sided. They extended to frontal, temporal, and parietal regions, anterior cingulate, insula, and putamen. These over-activations were slightly reduced and again more right sided two years after therapy. Left frontal deactivations remained stable over two years of observation, and therefore possibly indicate a dysfunction. After therapy, we noted higher activations in persons who stutter moderately than in those who stutter severely. These activations might reflect patterns of compensation. We discuss why these findings suggest that fluency-inducing techniques might synchronize a disturbed signal transmission between auditory, speech motor planning, and motor areas. EDUCATIONAL OBJECTIVES: The reader will learn about and be able to: (1) identify regions of brain activations and deactivations specific for PWS; (2) describe brain activation changes induced by fluency shaping therapy; and (3) discuss the correlation between stuttering severity and brain activation.

Adult↗

PubMed2003

Evidence for compensation for stuttering by the right frontal operculum.

There is recent evidence of focal alteration in fibre tracts underlying the left sensorimotor cortex in persistent developmental stuttering (PDS) [Lancet 360 (2002) 380]. If, as proposed, this anatomical abnormality is the cause of PDS, then overactivation in the right hemisphere seen with functional neuroimaging in stutterers may reflect a compensatory mechanism. To investigate this hypothesis, we performed two functional magnetic resonance imaging (fMRI) experiments. The first showed systematic activation of a single focus in the right frontal operculum (RFO) in PDS subjects during reading, which was not observed in controls. Responses in this region were negatively correlated with the severity of stuttering, suggesting compensation rather than primary dysfunction. Negative correlation was also observed during the baseline task that consisted in passive viewing of meaningless signs, indicating that RFO compensation acts independently of specific demands on motor speech output. The second experiment, that involved a covert semantic decision task, confirmed that RFO activation does not require overt utterances or motor output. In combination these findings suggest that the RFO serves a nonspecific compensatory role rather than one restricted to the final stages of speech production.

Adult↗