A stroke occurs when blood flow to a part of the brain is suddenly interrupted, often by a clot or a bleed, causing brain cells to die from lack of oxygen and nutrients. This event leads to physical and cognitive impairments reflecting the damaged area. A frequent observation is the sudden onset of weakness or paralysis on one side of the body (hemiparesis or hemiplegia). This specific pattern of unilateral weakness is rooted in the brain’s unique organization for controlling movement.
The Principle of Contralateral Control
The human brain is divided into two distinct hemispheres, the left and the right, which specialize in different functions. When controlling movement, the system is set up in a unique, crossed fashion. Voluntary movement originates primarily in the motor cortex, a strip of tissue located near the front of the brain in both hemispheres.
The nerve signals responsible for initiating movement travel down from the motor cortex through pathways known as the corticospinal tract. As these pathways descend toward the spinal cord, they cross over to the opposite side of the body within the lower brainstem. This anatomical feature is called decussation.
Because of this crossing, the right cerebral hemisphere controls the muscles on the left side of the body, and vice versa. If a stroke occurs in the right hemisphere, the resulting motor impairment manifests as weakness or paralysis on the body’s left side. This explains why an occlusion in a major vessel like the right middle cerebral artery commonly results in left-sided hemiplegia.
This contralateral organization is not limited to movement; the primary sensory pathways also cross over. The right hemisphere processes sensory information, such as touch and temperature, received from the left side of the body.
Core Functions of the Right Brain Hemisphere
Beyond motor control, the right hemisphere plays a role in spatial awareness and processing visual information. It allows a person to perceive the relationship between objects and their own body in space, which is necessary for accurate navigation, judging distances, and coordinating complex movements.
A specialization of the right brain involves broad, sustained attention to both the left and right sides of the environment. Unlike the left hemisphere, which focuses attention primarily on the right, the right hemisphere maintains a global focus on the entire visual field. It also helps process context and overall meaning in communication.
The right hemisphere is highly involved in interpreting non-verbal cues and the emotional content of communication. It processes prosody—the rhythm, stress, and intonation of speech—allowing a person to understand emotion conveyed through tone of voice. Recognizing facial expressions and body language also relies heavily on this hemisphere.
This side of the brain is also engaged in the processing and expression of emotion. It helps regulate emotional responses and is involved in appreciating humor and understanding abstract concepts.
Specific Deficits Following Right Hemisphere Stroke
Damage to the right hemisphere results in impairments extending beyond physical weakness on the left side of the body. The resulting cognitive and perceptual deficits profoundly affect a person’s perception of the world and their own condition, presenting unique rehabilitation challenges.
One striking non-motor symptom is spatial neglect, or hemi-inattention, which is a failure to acknowledge the left side of space. This is a profound deficit in attention, not vision, where the patient ignores everything on the left side. For example, a person with neglect may only eat food from the right half of their plate or fail to recognize their own paralyzed left arm.
Another complex symptom is anosognosia, an unawareness or denial of the stroke-related deficits. Patients may believe they can move their paralyzed left arm or walk normally, despite clear evidence. This lack of insight complicates therapeutic efforts and poses safety concerns, as they may attempt tasks beyond their current capability.
Impairments in visual-spatial processing are also common. Patients may struggle with depth perception, making tasks like pouring a drink or accurately placing objects difficult. Additionally, difficulties with topography, or navigating environments, can occur, meaning the patient may easily get lost.
Strokes affecting the right side of the brain can also lead to changes in behavior, often manifesting as impulsivity and poor judgment. Patients may rush through tasks or make quick decisions without considering the consequences, requiring careful supervision to prevent accidental injury.