Interhemispheric neuroplasticity following limb deafferentation detected by resting-state functional connectivity magnetic resonance imaging (fcMRI) and functional magnetic resonance imaging (fMRI)

Abstract

Functional connectivity magnetic resonance imaging (fcMRI) studies in rat brain show brain reorganization following peripheral nerve injury. Subacute neuroplasticity was observed two weeks following transection of the four major nerves of the brachial plexus. Direct functional magnetic resonance imaging (fMRI) stimulation of the intact radial nerve reveals an activation pattern in the forelimb regions of the sensory and motor cortices that is significantly different from that observed in normal rats. Results of this fMRI experiment were used to determine seed voxel regions for fcMRI analysis. Intrahemispheric connectivities in the sensorimotor forelimb representations in both hemispheres are largely unaffected by deafferentation, whereas substantial disruption of interhemispheric sensorimotor cortical connectivity occurs. In addition, significant intra-and interhemispheric changes in connectivities of thalamic nuclei were found. These are the central findings of the study. They could not have been obtained from fMRI studies alone-both fMRI and fcMRI are needed. The combination provides a general marker for brain plasticity. The rat visual system was studied in the same animals as a control. No neuroplastic changes in connectivities were found in the primary visual cortex upon forelimb deafferentation. Differences were noted in regions responsible for processing multisensory visual-motor information. This incidental discovery is considered to be significant. It may provide insight into phantom limb epiphenomena.

Optogenetic-guided cortical plasticity after nerve injury

“…Electrical stimulation of the forepaw consisted of 3 mA 300-μs pulses repeated at 3 Hz for 30 s (electrophysiology) and 20 s (optical imaging and fMRI). In agreement with previous studies (16,64), forepaw electrical stimulation at 9 Hz elicited consistent and robust fMRI responses compared with forepaw electrical stimulation at 3 Hz.…”

“…After craniotomy procedures, a bolus of dexmedetomidine (0.05 mg/kg s.c.) was given, and anesthesia was then maintained by a continuous infusion (0.1 mg/kg) (16,64). Images were acquired on a 9.4-T (Bruker) animaldedicated MRI system.…”

“…It is well-documented in humans (2), non-human primates (3), cats (4), and rodents (5-7) that peripheral nerve injury can lead to expansion of neighboring cortical representation of peripheral regions within the affected (deprived) hemisphere (intrahemispheric neuroplasticity). Peripheral nerve injury and direct cortical lesions have been shown to also modify functional communication between cortical hemispheres (interhemispheric neuroplasticity) (8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Specifically, peripheral inputs normally evoking neuronal responses in the contralateral hemisphere cause inappropriate functional responses in the ipsilateral hemisphere.…”

Imaging Neurovascular Function and Functional Recovery after Stroke in the Rat Striatum Using Forepaw Stimulation

“…6 This negative response has also been observed in epileptic rats during whisker stimulation 7 or normal rats during direct nerve stimulation. 8 Functional magnetic resonance imaging response has been shown to correlate better with local field potential (LFP) instead of spike; 9 however, whether this particular negative fMRI response matches with LFP changes remains unclear.…”

Cortical plasticity after brachial plexus injury and repair: a resting-state functional MRI study

“…Decreased interhemispheric functional connectivity between motor cortices in patients with complete unilateral BPI before surgery, revealed through the use of seed-based rs-fMRI, has been found in a few studies. 17,28 Qiu et al 29 used a seed-based rs-fMRI approach to demonstrate reduced resting-state functional connectivity (rsFC) between the supplementary motor area and motor cortical areas associated with the hand and arm contralateral to the injured side. This improvement over time despite no improvement in motor power was attributed to expansion of the adjacent cortical areas that encroach into the cortical areas that control the hand and arm.…”