Striosome

Striosomes, also known as matrix compartments or opiate receptor patches, are three-dimensional, heterogeneous zones within the dorsal striatum of the mammalian brain. They are characterized by distinct neurochemical properties and connectivity patterns compared to the surrounding matrix compartment. The striatum is a major input structure of the basal ganglia, a group of subcortical nuclei involved in motor control, habit formation, reward-based learning, and other cognitive functions.

Striosomes are identifiable through immunohistochemical staining, exhibiting high levels of certain substances like μ-opioid receptors (MORs), substance P, enkephalin, and dynorphin. Conversely, the surrounding matrix compartment is richer in calbindin and acetylcholine esterase. This neurochemical compartmentalization suggests different functional roles.

Striosomes receive afferent projections primarily from cortical regions involved in limbic and associative functions, including the prefrontal cortex, orbitofrontal cortex, anterior cingulate cortex, and amygdala. These cortical inputs are thought to carry information related to motivation, emotions, and decision-making. Efferent projections from striosomes target specific regions of the substantia nigra pars reticulata and globus pallidus pars interna, influencing the output of the basal ganglia and ultimately affecting motor and cognitive behaviors.

Functionally, striosomes are implicated in a variety of processes, including:

• Action Selection: Striosomes are thought to play a role in selecting appropriate actions based on internal states and contextual cues.
• Reward Processing: Their connection to limbic areas suggests involvement in processing reward-related information and motivational drive.
• Cognitive Flexibility: Striosomes may contribute to the ability to adapt behavior in response to changing environmental demands.
• Motor Control: By modulating basal ganglia output, striosomes can influence motor planning and execution.

Dysfunction of striosomes has been implicated in several neurological and psychiatric disorders, including Huntington's disease, Parkinson's disease, obsessive-compulsive disorder (OCD), and addiction. Research continues to explore the precise roles of striosomes in both normal brain function and disease states.