Cross-modal plasticity in deaf child cochlear implant candidates assessed using visual and somatosensory evoked potentials.

INTRODUCTION: Cross-modal plasticity has been extensively studied in deaf adults with neuroimaging studies, yielding valuable results. A recent study in our laboratory with deaf-blind children found evidence of cross-modal plasticity, revealed in over-representation of median nerve somatosensory evoked potentials (SEP N20) in left hemisphere parietal, temporal and occipital regions. This finding led to asking whether SEP N20 changes are peculiar to deaf-blindness or are also present in sighted deaf children. OBJECTIVE: Assess cross-modal plasticity in deaf child cochlear implant candidates using neurophysiological techniques (visual evoked potentials and median nerve somatosensory evoked potentials). METHODS: Participants were 14 prelingually deaf children assessed in the Cuban Cochlear Implant Program. Flash visual-evoked potentials and SEP N20 were recorded at 19 scalp recording sites. Topographic maps were obtained and compared to those of control group children with normal hearing. Analysis took into account duration of hearing loss. RESULTS: Topographic maps of flash visual-evoked potentials did not show changes in deaf child cochlear implant candidates. However, SEP N20 from right median nerve stimulation did show changes from expansion of cortical activation into the left temporal region in deaf children aged ≥7 years, which was interpreted as neurophysiological evidence of cross-modal plasticity, not previously described for this technique and type of somatosensory stimulus. We interpret this finding as due in part to duration of deafness, particularly related to handedness, since expansion was selective for the left hemisphere in the children, who were all right-handed. CONCLUSIONS: Cortical over-representation of SEP N20 in the left temporal region is interpreted as evidence of cross-modal plasticity that occurs if the deaf child does not receive a cochlear implant early in life-before concluding the critical period of neural development-and relies on sign language for communication.

Cross-modal plasticity in Cuban visually-impaired child cochlear implant candidates: topography of somatosensory evoked potentials.

INTRODUCTION: Studies of neuroplasticity have shown that the brain's neural networks change in the absence of sensory input such as hearing or vision. However, little is known about what happens when both sensory modalities are lost (deaf-blindness). Hence, this study of cortical reorganization in visually-impaired child cochlear implant (CI) candidates. OBJECTIVE: Assess cross-modal plasticity, specifically cortical reorganization for tactile representation in visually-impaired child CI candidates, through study of topography of somatosensory evoked potentials (SEP). METHODS: From April through September 2005, SEP from median and tibial nerve electrical stimulation were studied in 12 visually-impaired child CI candidates aged 3-15 years and 23 healthy controls. Following placement of 19 recording electrodes using the International 10-20 System , SEP were recorded and then processed. Topographic maps were obtained for SEP N20 (median nerve) and SEP P40 (tibial nerve), permitting assessment of cortical reorganization by comparing visually-impaired, deaf children's maps with those of healthy children by means of visual inspection and statistical comparison using a permutation test. RESULTS: SEP N20 topography was significantly more extensive in visually-impaired child CI candidates than in healthy children. An asymmetrical pattern occurred from the expansion of hand tactile activation into the temporal and occipital regions in the left hemisphere on right median nerve stimulation. This did not occur for SEP P40 on tibial nerve stimulation (right and left). Magnitude of expanded SEP N20 response was related to severity of visual impairment and longer duration of dual sensory loss. CONCLUSIONS: Changes in SEP N20 topography are evidence of cross-modal plasticity in visually-impaired child CI candidates, appearing to result from a complex interaction between severity of visual impairment and duration of multisensory deprivation.

Agnosia integrativa causada por una epilepsia focal occipital izquierda: estudio de caso / Integrative agnosia as a consequence of left focal occipital epilepsy: a case study

La agnosia integrativa es un tipo de agnosia visual asociada a lesiones occipitales bilaterales que se caracteriza por la incapacidad para identificar estímulos en fondos complejos, especialmente, cuando se trata de formas superpuestas o entrelazadas. Existen dificultades para codificar y agrupar el todo a partir de las partes del estímulo. Se presenta un caso de una paciente de 14 años, con una agnosia integrativa como consecuencia de una epilepsia focal sintomática refractaria, con un foco epileptogénico occipital izquierdo. Se plantean las características clínicas de la paciente y se hace un análisis de sus procesos de reconocimiento visual discutidos a partir de los diferentes modelos teóricos que tratan de explicar la percepción visual.

Integrative agnosia is a type of visual agnosia associated with bilateral occipital lesions and characterized by the inability to identify stimuli in complex backgrounds, especially when it comes to overlapping or interlocking shapes. There are difficulties in coding and grouping the whole from the parts of the stimulus. We report a case of a 14 year-old female, with integrative agnosia as consequence of refractory symptomatic focal epilepsy with left occipital epileptogenic focus. Clinical features and the visual recognition processes are analyzed and discussed from different theoretical models that attempt to explain visual perception.

Afasia de conducción como consecuencia de un astrocitoma anaplásico parieto–temporo–occipital izquierdo: estudio de caso / Conduction aphasia as a result of left parietal-temporal-occipital anaplastic astrocytoma: a case study

La afasia de conducción es un trastorno caracterizado por un lenguaje espontáneo relativamente fluido, buena comprensión, pero dificultades en la repetición asociadas con parafasias fonológicas. Se ha atribuido a lesiones del fascículo arqueado por desconexión entre el lóbulo temporal posterior y el frontal, sin embargo se ha debatido esta postura, planteando que la integridad y funcionamiento del fascículo arqueado no es indispensable en la repetición verbal. Se presenta un caso de un sujeto varón de 23 años que, como consecuencia de un astrocitoma anaplásico recidivante que abarca áreas parietales y temporo-occipitales, presenta una afasia de conducción. Se plantea una reconceptualización de esta afasia, analizándola en términos clínicos, neuropsicológicos y en las redes neuronales existentes entre áreas cerebrales posteriores ipsilaterales y contralaterales.

Conduction aphasia is a language disorder characterized by an impaired ability to repeat verbal material associated with phonological paraphasias but a relatively fluent spontaneous speech and preserved comprehension. It has been attributed to lesions of the arcuate fasciculus by disconnection between posterior temporal lobe and frontal lobe, however, this idea has been debated, because the integrity and function of the arcuate fasciculus does not seem to be essential in verbal repetition. We report a case of a 23 year old male, with conduction aphasia as a result of a recurrent anaplastic astrocytoma in parietal and temporo-occipital areas. We propose a reconceptualization of the aphasia, analyzing it in terms of clinical neuropsychological and neural networks between ipsilateral and contralateral posterior brain areas.