255 Auditory function in infants at risk for early brain damage

A138 Conclusion: We concluded that despite their epileptogenic activity, subcortical laminar heterotopia are responsible, in patients with such malformations of cortical development, for part of the functional activity of the brain, at least for their motor activity.

302 Reorganization of motor hand function to the contralesional hand area of the primary motor cortex in early unilateral brain damage G J M RUTTEN,’ H FRANSSEN,2 0 VAN NIEUWENHUIZEN,3 P C VAN RIJEN,’ C W M VAN VEELEN,’ N F RAMSEY4 Departments of Neurosurgery, ‘Clinical Neurophysiology, 3 Psychiatry, University Medical Centre, ‘Child Neurology, Utrecht, The Netherlands

Purpose: To determine locus of right-hand motor function in a patient with severe and extensive left-sided brain damage. To this purpose we studied motor function with functional MRl (fMRI), transcranial magnetic stimulation (TMS) and the sodium amytal (Wada) test. Background: Children with extensive unilateral brain lesions acquired in early life can learn to grasp for an object and walk, albeit with a limp. Imaging studies in these children have shown ipsilateral activation of motor function which is rarely seen in normal subjects. These observations suggest a cortical reorganization of motor functions to the contralesional hemisphere. Patient and methods: The patient is a K&year-old cognitively impaired left-handed girl with intractable partial epilepsy and extensive unilateral brain damage, probably due to a left perinatal stroke. She has spastic right hemiplegia with impaired fine motor control, but a relative mild paresis of proximal muscles. Three techniques were used to preoperatively investigate hand motor representation. (1) 3D BOLD fMRI (navigated PRESTO sequence), implemented on a Philips ACS-NT 1.5 T MRI scanner with standard hardware. The task consisted of active repetitive movements of the left and right hand respectively. Each task took 10 minutes of imaging time. (2) Transcranial magnetic stimulation (TMS) of the left and right central region. (3) Left hemisphere Wada test. Results: Significant increases in fMRI signal were observed for both tasks. Both normal as well as paretic hand movements selectively activated the right primary sensorimotor area, in the middle genu of the precentral gyrus. Superior mesenteric artery and lateral parts of the primary motor area were weakly activated bilaterally. TMS of the contralesional hemisphere induced bilateral responses in the median nerve but TMS of the lesioned hemisphere did not result in significant median nerve responses. The Wada test resulted in a slight increase in the paresis of the right hand. The patient is seizure-free 8 months after surgery and motor function equals preoperative motor functioning. Conclusion: The present data show that early extensive unilateral brain injury is associated with long-term reorganization of motor function to the contralesional hemisphere. Results from all three techniques confirm that ipsilesional motor function can be adopted by the contralesional primary motor cortex homologue.

Abstracts

255 Auditory damage

function

in infants at risk for early brain

J VATOVEC, M VELli3KOV12,

L SMID’

‘Department of Otorhinolaryngology and Cervicofacial Surgery, University Medical Centre, Ljubljana; 2Department of Developmental Neurology, University Paediatric Hospital, Ljubljana, Slovenija

Purpose: To identify hearing impairment in infants at risk for early brain damage. Some pre-, peri-, and postnatal risk factors for hearing loss are also risk factors for early brain damage. Our presumption was that the infants at risk for brain damage have hearing impairment more frequently than the rest of the population in the same age group and that the severity of neurological impairment coincides with the degree of hearing loss. Material and methods: 110 infants under 1 year of age who were at risk for brain damage underwent the following examinations: neurological examination, otorhinolaryngological examination, otoacoustic emission recoding, tympanometry, behavioural observation audiometry and when necessary auditory brainstem responses. The results of the audiological assessment were compared with the neurological findings. Results: Up to 32.7% of the examined infants did not have normal hearing. Sensorineural hearing loss was discovered in 7.3% and conductive hearing loss in 25.4% of examined infants. Those with abnormal neurological signs had permanent hearing impairment more often than those children with only neurological risk signs. Fisher test confirmed a statistically significant difference between these two groups (p = 0.02). Conclusion: Permanent hearing loss is more frequently present in infants at risk for brain damage than in their peers. Therefore all at-risk newborns and infants should be screened systematically for hearing impairment, especially as early detection of hearing loss is a prerequisite for successful habilitation.

299

The maturation of motor threshold and interhemispheric inhibition: A cross-sectional using magnetic stimulation

study

A ZIESEMER,’ J FIETZEK,’ J KIRSCHNER,’ F X GLOCKER,2 R KORINTHENBERG,’ F HEINEN’ ‘Department of Neuropaediatrics and Muscle Disorders; ‘Department of Neurology, University of Freiburg, Freiburg, Germany

Purpose: The excitability of cortical structures can be investigated using excitatory and inhibitory parameters. We used transcranial magnetic stimulation to measure interhemispheric inhibition (IhI) and motor threshold (MT). In the EMG the IhI shows as descreased motor activity in the ipsilateral muscles following a focal magnetic pulse to one hemisphere. It is primarily caused by transcallosal fibres which inhibit the contralateral motor cortex. However, since the cortical projecting neurons are excited through cortico-cortical interneurons, this method assesses both the maturation