title: A neuromorphic model of motor overflow in focal hand dystonia due to correlated sensory input.
abstract: Motor overflow is a common and frustrating symptom of dystonia, manifested as unintentional muscle contraction that occurs during an intended voluntary movement. Although it is suspected that motor overflow is due to cortical disorganization in some types of dystonia (e.g. focal hand dystonia), it remains elusive which mechanisms could initiate and, more importantly, perpetuate motor overflow. We hypothesize that distinct motor elements have low risk of motor overflow if their sensory inputs remain statistically independent. But when provided with correlated sensory inputs, pre-existing crosstalk among sensory projections will grow under spike-timing-dependent-plasticity (STDP) and eventually produce irreversible motor overflow.
  
  
  
  We emulated a simplified neuromuscular system comprising two anatomically distinct digital muscles innervated by two layers of spiking neurons with STDP. The synaptic connections between layers included crosstalk connections. The input neurons received either independent or correlated sensory drive during 4 days of continuous excitation. The emulation is critically enabled and accelerated by our neuromorphic hardware created in previous work.
  
  
  
  When driven by correlated sensory inputs, the crosstalk synapses gained weight and produced prominent motor overflow; the growth of crosstalk synapses resulted in enlarged sensory representation reflecting cortical reorganization. The overflow failed to recede when the inputs resumed their original uncorrelated statistics. In the control group, no motor overflow was observed.
  
  
  
  Although our model is a highly simplified and limited representation of the human sensorimotor system, it allows us to explain how correlated sensory input to anatomically distinct muscles is by itself sufficient to cause persistent and irreversible motor overflow. Further studies are needed to locate the source of correlation in sensory input.
authors: Department of Rehabilitation Medicine, Emory University, 1441 Clifton Rd, Atlanta, GA 30322, USA.
authors: Won Joon
authors: WJ
authors: Sohn
authors: Chuanxin M
authors: CM
authors: Niu
authors: Terence D
authors: TD
authors: Sanger
mesh_terms: D000465:Algorithms; D020821:Dystonic Disorders / Q000503:physiopathology*; D004525:Efferent Pathways / Q000503:physiopathology*; D004576:Electromyography; D005071:Evoked Potentials; D005385:Fingers / Q000294:innervation / Q000503:physiopathology; D006225:Hand / Q000503:physiopathology*; D006801:Humans; D008959:Models, Neurological; D018482:Muscle, Skeletal / Q000294:innervation / Q000503:physiopathology; D016571:Neural Networks, Computer; D009473:Neuronal Plasticity; D012677:Sensation; D013569:Synapses