A stroke occurs when the blood flow to a part of the brain is interrupted. This interruption can happen either due to a blocked blood vessel (ischemic stroke) or a ruptured one (hemorrhagic stroke). Brain cells, deprived of oxygen and nutrients, begin to die within minutes, leading to potential lasting damage. The specific symptoms experienced after a stroke depend entirely on which area of the brain is affected.
The Brain’s Cross-Wired Control
The human brain operates on a principle known as contralateral control, meaning each side of the brain primarily governs the opposite side of the body. The cerebrum, the largest part of the brain, is divided into two hemispheres: the left and the right. The right hemisphere largely controls the movements and sensations on the left side of the body, while the left hemisphere manages the right side.
This cross-wired organization extends to both motor functions, which involve movement, and sensory functions, which relate to feeling. When a stroke damages a specific area within one of these hemispheres, the resulting physical and cognitive effects are observed on the opposite side of the body.
When the Right Brain is Affected
A stroke affecting the right hemisphere of the brain leads to symptoms predominantly on the left side of the body. Physical manifestations include weakness or paralysis, a condition known as hemiparesis or hemiplegia, on the left side of the face, arm, and leg. Sensory loss, or a diminished ability to feel on the left side, is also a common occurrence.
Beyond physical impairments, right brain strokes can impact cognitive and behavioral functions. Individuals may experience spatial and perceptual difficulties, struggling with judging distances, understanding their position in space, or navigating their environment. This can manifest as left-sided neglect, where the person has a lack of awareness or attention to stimuli on their left side, even though their vision and hearing may be intact. For example, they might only eat food from the right side of a plate or bump into objects on their left.
Impulsivity is another behavioral change observed after a right brain stroke, particularly if the frontal lobe is involved. This can lead to a lack of forethought before acting, potentially compromising safety, as individuals may attempt activities they cannot safely perform. Additionally, difficulties with non-verbal communication are common, where affected individuals may struggle to interpret facial expressions, tone of voice, or sarcasm in others, and may also have trouble expressing these cues themselves. This can result in communication challenges that are more subtle than language deficits, but equally impactful on social interaction.
When the Left Brain is Affected (A Contrast)
In contrast, a stroke occurring in the left hemisphere of the brain results in symptoms on the right side of the body. This includes weakness or paralysis and sensory loss affecting the right arm, leg, and face. The left side of the brain is largely responsible for language processing in most individuals.
Consequently, a primary effect of a left brain stroke is aphasia, a disorder that impairs the ability to communicate. Aphasia can manifest as difficulty speaking, understanding language, reading, or writing. The specific type and severity of aphasia depend on the exact area of the left hemisphere damaged.