Pattern of cortical reorganization in amyotrophic lateral sclerosis: a functional magnetic resonance imaging study

Abstract

Depending on individual lesion location and extent, reorganization of the human motor system has been observed with a high interindividual variability. In addition, variability of forces exerted, of motor effort, and of movement strategies complicates the interpretation of functional imaging studies. We hypothesize that a general pattern of reorganization can be identified if a homogeneous patient population is chosen and experimental conditions are controlled. Patients with amyotrophic lateral sclerosis (ALS) and healthy volunteers were trained to perform a simple finger flexion task with 10% of each individual's maximum grip force with constant movement amplitude and frequency. The activation pattern in ALS patients was distinctly different to that in healthy controls: In ALS patients, motor cortex activation was located more anteriorly, encompassing the premotor gyrus. The cluster volume within the supplementary motor area (SMA) was higher and shifted toward the pre-SMA. Contralateral inferior area 6 and bilateral parietal area 40 revealed higher cluster volumes. Our results demonstrate a general pattern of functional changes after motor neuron degeneration. They support the concept of a structurally parallel and functionally specialized organization of voluntary motor control. Degeneration of the first and second motor neurons leads to enhanced recruitment of motor areas usually involved in initiation and planning of movement. Partial compensation between functionally related motor areas seems to be a strategy to optimize performance if the most efficient pathway is unavailable.

Neuroimaging in Amyotrophic Lateral Sclerosis

“…A general pattern of cortical reorganization was found for motor function in patients with ALS when compared with that seen in normal subjects [24], with increased activation of the contralateral sensorimotor cortex, supplementary motor area, basal ganglia, and cerebellum demonstrated on fMR images during motor tasks [24,25,80,81]. Increased sensorimotor activation has also been reported in the brain ipsilateral to the movement [80].…”

“…In the search for the UMN markers, several neuroimaging modalities, especially diffusion tensor imaging (DTI) [8][9][10][11][12][13][14][15][16], proton magnetic resonance spectroscopy ( 1 H-MRS) [14,15,[17][18][19][20], perfusion imaging [21], magnetization transfer imaging [22] (MTI) and functional magnetic resonance imaging (fMRI) [23][24][25], have been used with varying success. This article presents an overview of these neuroimaging methods and their potential roles in ALS.…”

Degeneration of the Human Nervous System and Magnetic Resonance Neuroimaging

“…A shift of activity to more anterior regions of the premotor cortex, i.e. Brodmann area (BA) 6, during upper limb movement has been observed in ALS patients (Konrad et al, 2002;Han et al, 2006), such findings being supported by previous functional imaging studies with PET (Kew et al, 1993a;. Furthermore, there is longitudinal fMRI evidence of progressive involvement of the premotor area in upper limb motor tasks in the course of the disease (Lulé et al, 2007a).…”

“…Konrad et al observed this in eleven ALS patients (Konrad et al, 2002) who performed a simple finger flexion task with 10% of each individual´s maximum grip force. Increased activity was found in motor areas such as the premotor area, supplementary motor area, and the cerebellum.…”

“…Furthermore, a changed pattern and an anterior shift of activity in ALS were also observed in further cortical areas besides the premotor cortex for various motor tasks. For instance, increased involvement of supplementary motor areas (SMA) (Konrad et al, 2002;2006;Han et al, 2006) and sensorimotor cortices has been seen (Brooks et al, 2000;Han et al, 2006;Stanton et al, 2007a;Mohammadi et al, 2011). Activity in contralateral sensorimotor cortex activity was increased the stronger the physical impairments were in patients .…”