The striatum is the largest structure within a set of deep brain nuclei known collectively as the basal ganglia. These nuclei are responsible for regulating voluntary movement, procedural learning, and the processing of rewards and motivation. The striatum acts as the main gateway for information entering the basal ganglia system from the cerebral cortex, serving as a hub where sensory, motor, and cognitive data are integrated. The dorsal striatum is divided into distinct subregions that handle different aspects of cognition and action selection. The dorsomedial striatum (DMS) is a specific area that plays a central role in purposeful behavior and flexible decision-making.
Anatomical Placement and Structure
The dorsomedial striatum is situated in the front and center portion of the dorsal striatum, corresponding broadly to the caudate nucleus and putamen in the human brain. This region maintains specific neural connections with other cortical areas, forming specialized circuits, and receives major input from the prefrontal cortex, particularly areas involved in association and planning. These connections are part of the cortico-basal ganglia-thalamic circuit, where information flows into the DMS, is processed, and then loops back to the cortex via the thalamus. The DMS is functionally distinct from its neighbor, the dorsolateral striatum (DLS), which primarily receives input from sensorimotor regions of the cortex.
The internal structure of the DMS is composed mainly of medium spiny neurons, the principal cell type of the striatum. These neurons receive excitatory signals from the cortex and modulatory signals from dopamine-producing neurons located in the midbrain. Dopamine signaling modulates synaptic plasticity, the process by which connections between neurons are strengthened or weakened based on experience.
Primary Cognitive Function: Goal-Directed Action
The DMS mediates goal-directed action, a sophisticated form of learned behavior. This function relies on the brain’s ability to form and maintain action-outcome (A-O) associations, which is the understanding that a specific action will lead to a desired result.
This contrasts with habitual behavior, which is mediated by the dorsolateral striatum and based on stimulus-response (S-R) associations. In goal-directed behavior, the action is performed because the outcome is currently valued; if the value changes, the action is quickly adjusted or stopped.
The learning process involves integrating the action, the specific outcome, and the current value of that outcome. Dopamine release in the DMS signals a reward prediction error—the difference between the expected and actual reward. This signal updates the value associated with the action, shaping the learning and performance of future purposeful behaviors. The DMS allows an organism to flexibly choose actions based on current needs and desires.
Role in Behavioral Flexibility and Decision Making
The DMS enables behavioral flexibility by applying action-outcome knowledge, allowing adaptation when environmental conditions change. This flexibility is necessary for strategic switching, enabling an individual to abandon an ineffective strategy and adopt a new one. Flexible action selection is important when decisions involve uncertain outcomes or multiple options.
The connectivity between the DMS and the prefrontal cortex supports this executive function. When a previously correct rule is reversed, the DMS must suppress the old association and rapidly encode the new one. Inactivation of the DMS impairs this reversal learning, causing individuals to struggle with maintaining the newly reinforced strategy.
The DMS integrates the organism’s internal state—such as hunger or motivation—with external cues to guide the selection of the most appropriate goal-directed action. This integration ensures that behavior is always aligned with the highest available value, making it a foundation of complex, adaptive decision-making.
Implication in Neurological Disorders
Dysfunction in the DMS and its associated circuits is implicated in several neurological disorders characterized by a loss of flexible control over behavior. One prominent example is the development of compulsive behaviors, hallmarks of obsessive-compulsive disorder (OCD) and substance use disorder. Compulsion is defined as the continued seeking of a reward even when that action is associated with a negative consequence, such as punishment.
Impairment in the DMS can cause a failure to disengage from reward-seeking behaviors, even when the outcome is no longer desirable or is actively harmful. Heightened dopamine activity within the DMS specifically predicts the transition to this punishment-resistant compulsive behavior. This highlights a mechanism where an overly active DMS system drives rigid, inflexible goal-seeking that has become maladaptive.
DMS impairment also contributes to the cognitive deficits seen in Parkinson’s disease. The degeneration of dopamine-producing neurons that project to the striatum impairs the ability to change goal-directed actions and shift strategies. This loss of DMS function contributes to the characteristic difficulty with cognitive flexibility, where the individual struggles to adapt their planning and decision-making to new situations.