Abstract
Degenerative cervical myelopathy (DCM) damages the spinal cord, resulting in long-term neurological impairment including motor and visual deficits. Given that visual feedback is crucial in guiding movements, the visual disorder may be a cause of motor deficits in patients with DCM. It has been shown that increased functional connectivity between secondary visual cortices and cerebellum, which are functionally related to the visually guided movements, was correlated with motor function in patients with DCM. One possible explanation is that the information integration between these regions was increased to compensate for impaired visual acuity in patients with DCM and resulted in better visual feedback during motor function. However, direct evidence supporting this hypothesis is lacking. To test this hypothesis and explore in more detail the information flow within the “visual-cerebellum” system, we measured the effective connectivity (EC) among the “visual-cerebellum” system via dynamic causal modeling and then tested the relationship between the EC and visual ability in patients with DCM. Furthermore, the multivariate pattern analysis was performed to detect the relationship between the pattern of EC and motor function in patients with DCM. We found (1) significant increases of the bidirectional connections between bilateral secondary visual cortices and cerebellum were observed in patients with DCM; (2) the increased self-connection of the cerebellum was positively correlated with the impaired visual acuity in patients; (3) the amplitude of effectivity from the cerebellum to secondary visual cortices was positively correlated with better visual recovery following spinal cord decompression surgery; and (4) the pattern of EC among the visual-cerebellum system could be used to predict the pre-operative motor function. In conclusion, this study provided direct evidence that the increased information integration within the “visual-cerebellum” system compensated for visual impairments, which might have importance for sustaining better motor function in patients with DCM.
Highlights
In clinical practice, degenerative cervical myelopathy (DCM) is a common disease, which results in compression of the cervical spinal cord, leading to numerous neurological dysfunctions, including sensory dysfunctions, fine motor deficits, and incontinence (Lebl et al, 2011; Akter and Kotter, 2018; Davies et al, 2018; Badhiwala et al, 2020)
We found that the functional connectivity (FC) between the dorsal visual stream regions [Brodmann Areas 7 (BA 7)] and the primary or secondary visual cortices (BA17/19) increased and associated with the impaired visual acuity in patients
We found that the self-connection of the cerebellum showed a significant correlation with the pre-operative visual acuities of bilateral eyes (Figures 4A,B); the unidirectional connectivity from the cerebellum to left secondary visual cortex correlated with the improvement of visual acuity of the left eye after spinal cord decompression surgery (Figure 4C); and the unidirectional connectivity from the cerebellum to right secondary visual cortex correlated with the improvement of visual acuity of the right eye after spinal cord decompression surgery (Figure 4D)
Summary
Degenerative cervical myelopathy (DCM) is a common disease, which results in compression of the cervical spinal cord, leading to numerous neurological dysfunctions, including sensory dysfunctions, fine motor deficits, and incontinence (Lebl et al, 2011; Akter and Kotter, 2018; Davies et al, 2018; Badhiwala et al, 2020). Several atypical symptoms including blurred vision, dizziness, headache, and tinnitus were frequently reported (Sun et al, 2013, 2016; Muheremu et al, 2016). Among these neurological symptoms, the loss of fine motor control of the hands is the most frequently encountered symptom (Kalsi-Ryan et al, 2013), causing difficulty in the daily life of patients. Our earlier study showed that the regional neural activities within visual cortices were altered and associated with the visual deficits in patients with DCM (Chen et al, 2018). Given that the visual feedback is crucial in the control of human movement (Sober and Sabes, 2005; Sarlegna et al, 2009; Goodale, 2011; Mizelle et al, 2016), visual impairments could be a crucial factor leading to motor deficits
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