18 July 2014
A new study by researchers at the University of Oregon (UO) details a brainstem circuit in mice that could help to explain how active movement can impact the way the brain processes sensory information.
The research, which has been published in the journal Neuron, was inspired by an event five years ago when examining visual perception in mice.
Cristopher Niell, a biology professor in the Institute of Neuroscience and the senior author on the paper entitled 'Identification of a Brainstem Circuit Regulating Visual Cortical State in Parallel with Locomotion', observed that running appeared to change how the brain's neurons were operating.
This initial finding, also published in the Neuron journal in 2010, found a connection between mind and body in the mouse's visual system. Following on from this discovery, the latest study sought to find the circuits within the brain that could link movement and vision together.
"Previous studies have examined changes in the visual cortex of mice during running. What was unknown was how do running and vision get linked together in the first place?" said Professor Niell.
"We found that running turned up the magnitude in the mouse's visual cortex by about two-fold - the signals were basically twice as strong when the mouse was running," he added.
The researchers focused on a specific part of the brain called the mesencephalic locomotor region (MLR), which has been shown to control running and other forms of activity in many species.
They hypothesised that the brain's pathways originating in the MLR could have two purposes: sending a signal down the spinal cord to start movement and another up to the brain's cortex to turn up the visual response.
The team then used genetically sensitised neurons in the MLR region of the mouse brain that could be activated by light and recorded the resulting increased visual responses in the cortex. They found that that the brain's MLR can indeed lead to both running and increased responsiveness in the cortex, and that these two effects could be dissociated, showing that they are controlled from different, separate pathways.
Stimulation in a region of the brain that sends neuromodulatory projections to the visual cortex caused changes in the cortex, but without physical activity. Interestingly, the basal forebrain is known to use the neuromodulator acetycholine, which is often associated with alertness and attention.
It is still unclear whether humans experience heightened visual perception when running, but the study adds to growing evidence that active movement is linked to sensory processing in the brain. Similar regions have been targeted in humans for therapeutic deep-brain stimulation to treat motor dysfunction in patients with Parkinson's disease. Activating this circuit might also provide a means to enhance neuroplasticity, the brain's capacity to rewire itself.
Professor Niell's team included Moses Lee, a visiting scholar at the UO and student in the MD-Ph.D. programme at UC-San Francisco, who served as the lead author on the paper. "While it seems that moving and sensing are two independent processes, a lot of new research suggests that they are deeply coupled," Mr Lee said. "My hope is that our study can help solidify our understanding of how the brain functions differently in 'alert' states."
Posted by Edward Bartel
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