Functional magnetic resonance imaging (fMRI) clinical studies in ALS - paradigms, problems and promises

Abstract

Functional magnetic resonance imaging (fMRI) provides high-resolution, non-invasive estimates of neural activity detected by a blood oxygen level dependent signal by assessing the increase in blood flow to the local vasculature that accompanies neural activity in the brain. fMRI studies with standard hand motor test (index-thumb opposition, ITO, or pinch) in ALS patients show good test-retest reliability and similar amplitude of signals in ALS patients compared with control subjects. Isometric force can be performed with careful control for the force exerted, recruitment of other muscles and motion artefact. The volume (number of voxels above threshold) of sensorimotor and cerebellar cortex activated by ITO is reproducibly larger in ALS patients compared with control subjects. Imagined movements in ALS have been studied, as in amputees, and larger volumes are activated in ALS patients with imagined movements as well, compared with control subjects. fMRI studies in ALS patients evaluating cortical activation during pure somatosensory stimulation cutaneous stimulation of the hand to elicit the palmomental response and cutaneous stimulation of the sole to elicit the plantar response - indicate that ALS patients activate a significantly smaller volume of the contralateral sensorimotor cortex compared to control subjects. No statistically significant difference was seen in other areas, including the ipsilateral cerebellum and the contralateral thalamus. An anterior shift in the volume of cortex activated by these paradigms occurs in ALS patients, with a volume of activation, anteriorly, not activated in control subjects. fMRI studies will complement other clinical neurophysiological and neuroimaging techniques in our future attempts to solve the riddle of ALS and other motor neuron diseases.

Neuroimaging in Amyotrophic Lateral Sclerosis

“…The MR spectrum is a spectral graph in which the x-axis denotes the unique chemical composition of a metabolite in parts per million (ppm) and the y-axis reflects the concentration of that metabolite. Although the MR spectrum can be generated from any element in the periodic table that has an odd number of protons, biological MR studies are generally confined to those involving the 1 H, 31 P, 13 C, 23 Na, and 19 F protons. Of these, the most commonly studied is proton ( 1 H) nucleus due to its abundance in biological tissue (water and fat) and high sensitivity.…”

“…Since deoxyhemoglobin is paramagnetic, it alters the T2*-weighted magnetic resonance image signal. Therefore, this change leads to an increase in the fMRI signal that has been called the blood oxygenated level-dependent effect [23,79].…”

“…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

“…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 .…”

“…In fMRI studies, ALS patients present higher volumes of activated brain areas in motor tasks compared with healthy controls, thus providing evidence for functional reorganisation and cortical plasticity in MND (Brooks et al, 2000;Lulé et al, 2009). 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.…”