Neuroimaging of multimodal sensory stimulation in amyotrophic lateral sclerosis

Structural and functional imaging techniques were combined to investigate sensory system function in amyotrophic lateral sclerosis (ALS).

Functional MRI (fMRI) was used to investigate cortical activity during visual, auditory and somatosensory stimulation in 14 ALS patients and 18 control subjects. Changes in amplitude, latency and duration of the blood oxygen level dependent response were modelled. Furthermore, diffusion tensor imaging was used to investigate changes in white matter networks.

During visual stimulation, fMRI demonstrated a decreased response in secondary visual areas in ALS, possibly related to demyelination of sensory nerve fibres. Increasing brain activity in associative cortices was linked to a decrease in physical functioning and might represent a compensatory process. Additionally, reduced white matter functioning became evident for fibres projecting to the extrastriate visual cortex. For auditory stimulation, a delayed response in secondary auditory areas probably linked to prolonged nerve conductance time and an altered cortical pattern in areas involved in target processing/detection became evident in ALS patients. Structural white matter changes in the primary and secondary auditory cortices were observed. For somatosensory stimulation, a prolonged/reduced response in sensory integration areas of the parietal lobe was observed, perhaps linked to the reduced visceral inflow due to immobility.

Multiparametric MRI suggests a progressive functional deficit in secondary/higher order sensory processing areas in ALS, probably associated with reduction of re-afferent information flow due to progressive immobility. The changes described might also represent an expression of the disease process itself. Evidence for compensatory processes in multimodal associative cortices was found.