Tracking Neuron Motor Encoding in the Striatum

     In Wambura C. Fobbs' article, Continuous Representations of Speed by Striatal Medium Spiny Neurons, her research focuses on neural motor encoding in the Striatum. The striatum is a component of the basal ganglia that receives information about possible actions from the motor cortex. Previous research has shown that the striatum area of the brain is critical for motor output, but Fobb's research aims to prove their hypothesis that striatal neurons follow a discrete encoding model. This model suggests that neurons facilitate movements with brief bursts of activity near the start and end of movements.

    To test this hypothesis, Fobb's team used mice as a test subject for neuronal activity. These mice had electrode implantations in the right dorso-medial striatum (DMS). The mice where then allowed to move freely in an arena while researchers recorded single and multi-units from the DMS. From these recording they found, "that a larger percentage of striatal neurons participated in a continuous representation than in discrete signaling" (Fobbs, 1680). This evidence was produced by multiple types of locomotion such as: digging, grooming, rearing, resting, and walking. In this experiment the researchers also measured the speed distribution of neuron activity during these locomotions. Using the same electrodes, they found that 18% of the DMS units increased in firing near the start of locomotion. They also found that 15% of the units increased in firing during the end of locomotion. Fobbs urges that these findings illustrate a linear relationship between speed and striatal neuron activity. Thus, supporting the discrete encoding model of neuronal activity that is proposed by Fobbs.

    The research conducted by Fobbs and her team portray relevant evidence for the mechanisms of striatum neuron activity. Another article I found that relates to this topic is by the author Mo Costandi. His piece, Movement Maps Found Deep Inside the Brain,  discusses research that also observes the striatal activity of mice. Though, in this study the researchers implanted mice with a calcium sensor that emits fluorescent light in response to when calcium concentrations increase. They were able to visualize the activity of striatal neurons in the mice during free movement. Costandi states his main finding in the article. The finding is that "neurons that are closer together, are more likely to be active together." (Costandi, 1). Costandi's findings reinforce the idea that neurons closer together will produce similar neuronal activity. This info also supports Fobb's model of discrete encoding because the neurons will activate in distinct locations and similar neuronal concentrations.

    This research is relevant for modern health because there are many human diseases and injuries that can disturb the neuronal pathways of movements. It is important to consider the activity and mechanism of motor neurons so scientists can help prevent or cure diseases like Parkinson's. This disease affects nerve cells in the basal ganglia (striatum nerves), so research like Fobb's and Costandi' are imperative. By studying the neuronal activity of mice, these researchers are steps closer to solving the functional mechanisms of motor neuron activity. 

Costandi, Mo. “‘Movement Maps’ Found Deep inside Brain.” Scientific American, Scientific American, 30 Aug. 2017, https://www.scientificamerican.com/article/movement-maps-found-deep-inside-brain/. 

Fobbs, Wambura C. “Continuous Representations of Speed by Striatal Medium Spiny Neurons.” The Journal of Neuroscience, vol. 40, no. 8, 2020, pp. 1679–1688., https://doi.org/10.1523/jneurosci.1407-19.2020.