Date of Award
Doctor of Philosophy (PhD)
Brain circuits are shaped and maintained by active use. We blocked use of motor circuits in three adult participants by constraining the dominant upper extremity in a cast for two weeks, causing loss of strength and fine motor function. Daily resting-state functional magnetic resonance imaging (rs-fMRI) collected for 42-64 days before, during and after casting revealed two sets of changes in brain function. First, large, spontaneous pulses of activity occurred in the disused motor circuits. Pulses showed a consistent pattern of propagation through the disused circuits— occurring earliest in the dorsal anterior cingulate cortex (dACC) and supplementary motor area (SMA), then propagating to the primary motor cortex, and finally occurring in motor regions of the cerebellum. Second, participants exhibited anatomically focal changes in functional connectivity (FC), i.e., synchrony of spontaneous activity. The disused motor cortex lost typical FC with the remainder of the somatomotor system. Additionally, disused regions of the primary motor cortex and cerebellum became more connected to an executive control system known as the cingulo-opercular network (CON). Spontaneous activity pulses, which occurred in disused motor regions and the CON, accounted for observed increases in FC. Loss of FC between the disused motor circuits and the somatomotor network was not explained by pulses and may have resulted from decreased co-use of the affected circuits with the remainder of the somatomotor system, which is typically thought to maintain FC in a Hebbian-like manner. Together, these two forms of plasticity, Hebbian disconnection from the somatomotor system and pulse-mediated connection to the CON, may form a protective “standby mode” that isolates disused circuits and prevents premature functional degradation.
Chair and Committee
Newbold, Dillan James, "Disuse-Driven Plasticity in the Human Brain" (2022). Arts & Sciences Electronic Theses and Dissertations. 2684.