title: Increased long-latency reflex activity as a sufficient explanation for childhood hypertonic dystonia: a neuromorphic emulation study.
abstract: OBJECTIVE
  Childhood dystonia is a movement disorder that interferes with daily movements and can have a devastating effect on quality of life for children and their families. Although injury to basal ganglia is associated with dystonia, the neurophysiological mechanisms leading to the clinical manifestations of dystonia are not understood. Previous work suggested that long-latency stretch reflex (LLSR) is hyperactive in children with hypertonia due to secondary dystonia. We hypothesize that abnormal activity in motor cortices may cause an increase in the LLSR leading to hypertonia.
  
  
  METHODS
  We modeled two possibilities of hyperactive LLSR by either creating a tonic involuntary drive to cortex, or increasing the synaptic gain in cortical neurons. Both models are emulated using programmable very-large-scale-integrated-circuit hardware to test their sufficiency for producing dystonic symptoms. The emulation includes a joint with two Hill-type muscles, realistic muscle spindles, and 2,304 Izhikevich-type spiking neurons. The muscles are regulated by a monosynaptic spinal pathway with 32 ms delay and a long-latency pathway with 64 ms loop-delay representing transcortical/supra-spinal connections.
  
  
  RESULTS
  When the limb is passively stretched, both models produce involuntary resistance with increased antagonist EMG responses similar to human data; also the muscle relaxation is delayed similar to human data. Both models predict reduced range of motion in voluntary movements.
  
  
  CONCLUSIONS
  Although our model is a highly simplified and limited representation of reflex pathways, it shows that increased activity of the LLSR is by itself sufficient to cause many of the features of hypertonic dystonia.
authors.affiliation: Department of Biomedical Engineering, University of Southern California, 1042 Downey Way, Los Angeles, CA 90089, USA.
authors.forename: Won J
authors.initials: WJ
authors.lastname: Sohn
authors.forename: Chuanxin M
authors.initials: CM
authors.lastname: Niu
authors.forename: Terence D
authors.initials: TD
authors.lastname: Sanger
mesh_terms: D040761:Biomimetic Materials; D002648:Child; D003198:Computer Simulation; D004867:Equipment Design; D019544:Equipment Failure Analysis; D025461:Feedback, Physiological; D006801:Humans; D008959:Models, Neurological; D009044:Motor Cortex / Q000503:physiopathology*; D009068:Movement; D009119:Muscle Contraction; D009122:Muscle Hypertonia / Q000503:physiopathology*; D018482:Muscle, Skeletal / Q000503:physiopathology; D011930:Reaction Time; D012026:Reflex, Stretch