Think about a person performing a simple action, when they reach for a pan of brownies, a ball-shaped brain structure called the striatum is critical for controlling their movement toward the reward. A healthy striatum also helps a person stop when they’ve had enough; however, when the striatum misfunctions, it can lead to disorders such as Parkinson’s disease, obsessive-compulsive disorder and/or addiction.  It is for this reason that the exact functions of the striatum, and its coordination of many diverse functions, are such a highly researched area. Now, a study from researchers at the Salk Institute identifies new striatal circuitry, and redefines the neuronal components of the striatum.  The team state that the global medical community has a new avenue to study long-standing questions about how the striatum controls movement in both healthy and diseased brains. The opensource study is published in the journal Neuron.

Previous studies show that forty-years ago, researchers discovered the unique way that the striatum is organized. It is dotted with patch neurons, which under the microscope look like tiny islands of cells. The ocean surrounding them is made up of neurons collectively referred to as ‘matrix’ cells.  Over the course of four decades, many studies hypothesized about the role of patch and matrix neurons in neurodegenerative diseases. One idea was that patch cells were fed by the brain’s higher thought centres, suggesting they could play a role in cognition, whereas the matrix cells seemed to play a role in sensing and movement.  The current study shows that both types of information are sent to the patch and matrix neurons, though patch cells tend to receive slightly more information from the brain’s emotion centers, included in the higher thought centres.

The current study uses transgenic mice to map brain-wide differences in the input-output organization of the patch and matrix neurons. Results show a displaced population of striatal ‘exo-patch’ neurons which reside in matrix zones, with the neurochemistry, connectivity, and electrophysiological characteristics resembling patch neurons.  Data findings show patch/exo-patch and matrix neurons receive both limbic and sensorimotor information, contrary to many past studies.

The lab state that their findings could help explain why, in the brains of patients with neurological disorders such as Huntington’s disease, both patch cells and matrix cells are affected. They go on to add that their findings redefine patch/matrix neurons beyond traditional neurochemical topography and reveal new principles about their input-output connectivity, providing a foundation for future functional studies.

The team surmise that their findings show both patch and matrix groups contain both indirect and direct pathway cells. For the future, the researchers state their data makes the story of the striatum more complicated, however, they now plan to study the intersection of these two types of organizational neurons in the context of how the striatum controls actions in health and disease.

Source: The Salk Institute