Extensive peri-lesional connectivity in congenital hemiparesis

Principles of early intervention

The great majority of children with neurodevelopmental challenges do not get specific intervention until after their second birthday. This worsens their outcomes, because a great part of the entire neuroplastic window for learning is misspent. There is emerging evidence that the impact on outcomes of early goal-directed training involving the parents in infants with neurodevelopmental disabilities is significantly superior to the results achieved in older children and adults, especially if intervention commences in the first months of life. This chapter outlines the common elements of neurodevelopment and early intervention. It includes an outline of some of the primary early intervention practices and the scientific evidence driving them.

Reactivity of sensorimotor oscillations is altered in children with hemiplegic cerebral palsy: A magnetoencephalographic study

Cerebral palsy (CP) is characterized by difficulty in control of movement and posture due to brain damage during early development. In addition, tactile discrimination deficits are prevalent in CP. To study the function of somatosensory and motor systems in CP, we compared the reactivity of sensorimotor cortical oscillations to median nerve stimulation in 12 hemiplegic CP children vs. 12 typically developing children using magnetoencephalography. We also determined the primary cortical somatosensory and motor representation areas of the affected hand in the CP children using somatosensory-evoked magnetic fields and navigated transcranial magnetic stimulation, respectively. We hypothesized that the reactivity of the sensorimotor oscillations in alpha (10 Hz) and beta (20 Hz) bands would be altered in CP and that the beta-band reactivity would depend on the individual pattern of motor representation. Accordingly, in children with CP, suppression and rebound of both oscillations after stimulation of the contralateral hand were smaller in the lesioned than intact hemisphere. Furthermore, in two of the three children with CP having ipsilateral motor representation, the beta- but not alpha-band modulations were absent in both hemispheres after affected hand stimulation suggesting abnormal sensorimotor network interactions in these individuals. The results are consistent with widespread alterations in information processing in the sensorimotor system and complement current understanding of sensorimotor network development after early brain insults. Precise knowledge of the functional sensorimotor network organization may be useful in tailoring individual rehabilitation for people with CP.

Relationship between functional connectivity and sensory impairment: red flag or red herring?

Resting-state functional magnetic resonance imaging (fMRI) can be used to study the functional connectivity in the somatosensory system. However, the relationship between sensory network connectivity, sensory deficits, and structural abnormality remains poorly understood. Previously, we investigated the motor network in children with congenital hemiparesis due to middle cerebral artery strokes (MCA, n = 6) or periventricular lesions (PL, n = 8). In the present study, we validate the use of interleaved resting-state data from blocked fMRI designs to investigate the somatosensory network in these patients. The approach was validated by assessing the predicted "crossed-over" connectivity between the cerebral cortex and the cerebellum. Furthermore, the impact on the volume of gray-matter (GM) in primary (S1) and secondary (S2) somatosensory cortex on functional connectivity measures was investigated. We were able to replicate the well-known "crossed-over" pattern of functional connectivity between cerebral and cerebellar cortex. The MCA group displayed more sensory deficit and significantly reduced functional connectivity in the lesioned S2 (but not in lesioned S1) when compared with the PL group. However, when accounting for GM volume loss, this difference disappeared. This study demonstrates the applicability of analyzing resting-state connectivity in patients with brain lesions. Reductions of functional connectivity within the somatosensory network were associated with sensory deficits, but were fully explained by the underlying GM damage.

Reorganization after pre- and perinatal brain lesions

The developing human brain can compensate for pre- and perinatally acquired focal lesions more effectively than the adult brain. The mechanisms by which this effective reorganization is achieved vary considerably between different functional systems, reflecting differences in the normal maturation of these systems. In the motor system, descending cortico-spinal motor projections have already reached their spinal target zones at the beginning of the third trimester of pregnancy, with initially bilateral projections from each hemisphere. During normal development, the ipsilateral projections are gradually withdrawn, whereas the contralateral projections persist. When, during this period, a unilateral brain lesion disrupts the cortico-spinal projections of one hemisphere, the ipsilateral projections from the contralesional hemisphere will persist. This allows the contralesional hemisphere to take over motor control over the paretic extremities. Although this mechanism of reorganization is available throughout the pre- and perinatal period, the efficacy of this ipsilateral takeover of motor functions decreases with increasing age at the time of the insult. In the somatosensory system, ascending thalamo-cortical somatosensory projections have not yet reached their cortical target zones at the beginning of the third trimester of pregnancy. Therefore, these projections can still 'react' to brain lesions acquired during this period, and can form 'axonal bypasses' around periventricular white matter lesions to reach their original cortical target areas in the postcentral gyrus. Thus, somatosensory functions can be well preserved even in cases of large periventricular lesions. In contrast, when the postcentral gyrus itself is affected, no signs for reorganization have been observed. Accordingly, somatosensory functions are often poor in these patients. Language functions can be normal even in patients with extensive early left-hemispheric brain lesions. This is achieved by language organization in the right hemisphere, which takes place in brain regions homotopic to the classical left-hemispheric language areas in normal subjects. In patients with periventricular lesions, the degree of right-hemispheric takeover of language functions correlates with the severity of structural damage to facial (and, thus, articulatory) motor projections.

Brain plasticity following early life brain injury: insights from neuroimaging

The developing human brain possesses a superior capacity to reorganize after focal lesions. This review describes mechanisms of reorganization following pre- and perinatally-acquired, unilateral brain lesions for motor, somatosensory, and language functions. In the motor system, unilateral damage to the corticospinal tract can lead to the maintenance of normally-transient ipsilateral corticospinal projections from the contralesional hemisphere. In some patients, this type of corticospinal (re)organization can achieve an active grasp function of the paretic hand, while in others no useful hand function develops although such projections exist. In the somatosensory system, periventricular lesions can be compensated by outgrowing thalamocortical projections forming "bypasses" around the defective white matter to reach the postcentral gyrus. By contrast, lesions in the postcentral gyrus often lead to marked somatosensory deficits. Finally, language functions can be taken over by the right hemisphere in cases of left hemispheric damage, often with excellent functional outcome. Knowledge of these mechanisms is necessary for establishing a "prognostic corridor" of development derived from neuroimaging in newborns with brain lesions.

Do patients with congenital hemiparesis and ipsilateral corticospinal projections respond differently to constraint-induced movement therapy?

This study investigates whether the type of corticospinal reorganization (identified by transcranial magnetic stimulation) influences the efficacy of constraint-induced movement therapy (CIMT). Nine patients (five males, four females; mean age 16y [SD 6y 5mo], range 11-30y) controlling their paretic hand via ipsilateral corticospinal projections from the contralesional hemisphere and seven patients (three males, four females; mean age 17y [SD 7y], range 10-30y) with preserved crossed corticospinal projections from the affected hemisphere to the paretic hand underwent 12 consecutive days of CIMT. A Wolf motor function test applied before and after CIMT revealed a significant improvement in the quality of upper extremity movements in both groups. Only in patients with preserved crossed projections, however, was this amelioration accompanied by a significant gain in speed, whereas patients with ipsilateral projections tended to show speed reduction. These data, although preliminary, suggest that patients with congenital hemiparesis and ipsilateral corticospinal projections respond differently to CIMT.

[Magnetoencephalography: a method for the study of brain function in neurosurgery]

Magnetoencephalography (MEG) is a non-invasive method for the study of electro-magnetic brain activity. Using multi-channel recordings the topography of the magnetic field can be recorded above the scalp with a temporal resolution of less than one millisecond. The method is suitable for the description and localization of cortical brain functions. The magnetic field strength that can be measured at up to 300 sensors is in the range of a few femto Tesla (10(-15) T) to somepico Tesla (10(-12) T). In order to measure these low magnetic fields highly sensitive SQUID-detectors are used on the one hand. On the other hand appropriate shielding equipment is employed to reduce effects of noise. Besides brain responses evoked by internal and external events (event-related magnetic fields), state-dependant oscillatory brain activity MEG can be recorded (spontaneous activity). Slow cortical oscillations in the range of 1 to 4 Hz are generated by damage of brain tissue and in the surrounding of brain tumors. In neurosurgery these activities can be used to monitor therapeutic success. Furthermore, oscillatory activities provide information about cortical regions involved in motor control. The measurement of motor related activities allows for the identification of recovery processes and reorganization after brain injury. Event-related magnetic brain responses are used in pre-surgical diagnosis and planning of treatment in epilepsy. In addition, they can be utilized to assess alterations in the functional organization of the cortex following injuries, tumor growth and neurosurgical interventions.

Reorganisation of the somatosensory system after early brain damage

OBJECTIVE

To examine the reorganisation of the somatosensory system after early brain lesions.

METHODS

We studied 12 young patients with congenital hemiplegia. Causative lesions were brain malformations, periventricular injuries and cortico-subcortical lesions. We explored the somatosensory system using evoked potentials, fMRI during sensory stimulation and clinical assessment of sensory function. To correlate sensory and motor function, we also performed transcranial magnetic stimulation, fMRI of hand movement and assessment of motor function by means of Melbourne test.

RESULTS

Eleven patients showed a perilesional reorganisation of primary somatosensory function, as expressed by short latency potentials following stimulation of the paretic hand; in a remaining patient, delayed latency responses (N27.1) were only elicited over the ipsilateral undamaged hemisphere. Five of the eleven patients with perilesional somatosensory representation of the affected hand showed contralesional shifting of motor function, thus exhibiting sensory-motor dissociation. Significant correlation was found between sensory deficit and fMRI activation during sensory stimulation.

CONCLUSIONS

In subjects with early brain lesions, somato-sensory function is generally reorganised within the affected hemisphere. A contralesional shifting is uncommon and poorly efficient in function restoration.

SIGNIFICANCE

This study confirms and further explores the difference in reorganisation capabilities of the motor and sensory system following early brain injury of different etiologies and timing.