Essential tremor is a neurological syndrome of heterogeneous pathology and 
aetiology that is characterized by tremor primarily in the upper extremities. 
This tremor is commonly hypothesized to be driven by a single or multiple neural 
oscillator(s) within the cerebello-thalamo-cortical pathway. Several studies 
have found an association of blood-oxygen level-dependent (BOLD) signal in the 
cerebello-thalamo-cortical pathway with essential tremor, but there is 
behavioural evidence that also points to the possibility that the severity of 
tremor could be influenced by visual feedback. Here, we directly manipulated 
visual feedback during a functional MRI grip force task in patients with 
essential tremor and control participants, and hypothesized that an increase in 
visual feedback would exacerbate tremor in the 4-12 Hz range in essential tremor 
patients. Further, we hypothesized that this exacerbation of tremor would be 
associated with dysfunctional changes in BOLD signal and entropy within, and 
beyond, the cerebello-thalamo-cortical pathway. We found that increases in 
visual feedback increased tremor in the 4-12 Hz range in essential tremor 
patients, and this increase in tremor was associated with abnormal changes in 
BOLD amplitude and entropy in regions within the cerebello-thalamo-motor 
cortical pathway, and extended to visual and parietal areas. To determine if the 
tremor severity was associated with single or multiple brain region(s), we 
conducted a birectional stepwise multiple regression analysis, and found that a 
widespread functional network extending beyond the cerebello-thalamo-motor 
cortical pathway was associated with changes in tremor severity measured during 
the imaging protocol. Further, this same network was associated with clinical 
tremor severity measured with the Fahn, Tolosa, Marin Tremor Rating Scale, 
suggesting this network is clinically relevant. Since increased visual feedback 
also reduced force error, this network was evaluated in relation to force error 
but the model was not significant, indicating it is associated with force tremor 
but not force error. This study therefore provides new evidence that a 
widespread functional network is associated with the severity of tremor in 
patients with essential tremor measured simultaneously at the hand during 
functional imaging, and is also associated with the clinical severity of tremor. 
These findings support the idea that the severity of tremor is exacerbated by 
increased visual feedback, suggesting that designers of new computing 
technologies should consider using lower visual feedback levels to reduce tremor 
in essential tremor.