Years ago, I became interested in Parkinson’s disease. I had always been obsessed with sport, but from there emerged a fascination with how improving movement in both athletes and people with Parkinson’s might share the same principles.
I didn’t set out to investigate this in our paper. Rather, we wanted to make sense of a now large literature on sensory attenuation with a particular interest in Parkinson’s symptoms, which sensory attenuation has been used to explain.
Sensory attenuation captures a fundamental aspect of sensorimotor integration, and how we as living systems inevitably interact with our environment at every moment. In the paper we define sensory attenuation as the distinct processing of an identical stimulus in two different contexts.
Framing the investigation with an interest in Parkinson’s brought the role of the basal ganglia into sharp focus. I believe, despite its evasiveness, we have communicated just a sense of the true function of the basal ganglia.
There is a dual effect of BG dysfunction in PD where a reduced ability to filter relevant signals from a complex environment overwhelms a BG system already at reduced capacity, just when contextual cues might be used to enhance movement and perceptionKearney & Brittain, 2021, p.14
We argue that the basal ganglia filter the complex, dynamic environment (both information from the body and the external surroundings) first in a task-relevant manner; then, such filtered signals act as useful contextual cues for enhanced action or perception.
This description of the basal ganglia helps make sense of the sensory attenuation data too, where task is not often considered in experiment paradigms, and therefore movement (for example), is expected to have a uniform effect on sensation. Instead, our body position and movement can attenuate or facilitate a stimulus depending on the task.
In this review then, we make sense of existing data surrounding a phenomenon that has been argued to be important in the symptoms of Parkinson’s disease and captures key fundamentals of how our brains process sensory information. We argue it is less important whether or not a stimulus is attenuated or facilitated, but rather the degree to which it is modulated. The direction (attenuation vs facilitation) will depend on the task, and the magnitude will depend on the utilisation of contextual information.
Secondly, we believe we shed light on some of the things the basal ganglia get up to. This includes incorporating disparate signals from across the brain to filter complex environments, helping to effectively move and remain in the moment amidst uncertainty, without the need for “pre-filtered” cues.
This poses a challenge, but as no two contexts of a movement are ever the same, perhaps it is better to train the underlying ability to identify and utilise contextual cues and to do so in a range of interesting environments that invite exploration and the use of task-relevant filtering to draw out cues to enhance movement.Kearney & Brittain, 2021, p.13
Finally, we move towards establishing principles for effective rehabilitation in Parkinson’s. This part is something I’m proud of, drawing a novel connection between sport and Parkinson’s rehabilitation, which I pondered years ago.