A stroke occurs when blood flow to a part of the brain is disrupted, either by a blockage (ischemic stroke) or a burst blood vessel (hemorrhagic stroke). This interruption deprives brain cells of oxygen and nutrients, leading to damage. While motor and cognitive impairments are widely recognized effects, a less common consequence is the development of hallucinations. These sensory disturbances involve perceiving something that is not actually present.
Confirmation and Types of Post-Stroke Hallucinations
Hallucinations are perceptions experienced without an external stimulus and can affect any of the five senses. Following a stroke, the estimated frequency of experiencing delusions or hallucinations is around 5%. These experiences are directly linked to damaged sensory pathways within the brain.
Visual hallucinations are the most reported type and often present as complex, formed images rather than simple flashes of light. Patients may see detailed pictures of people, animals, or entire scenes that they understand are not real, a phenomenon sometimes associated with Charles Bonnet syndrome. Auditory hallucinations involve hearing sounds like music or voices when no one is speaking, pointing to damage in the brain’s sound-processing regions.
Less frequently, a stroke may cause tactile or somatic hallucinations, where a person feels sensations of touch, movement, or pain without a physical cause. For example, a person might feel insects crawling on their skin or a limb moving when it is still.
Neurological Basis: How Stroke Location Causes Sensory Disruption
The occurrence and nature of hallucinations depend on the specific location of the stroke within the brain’s sensory network. Damage to an area responsible for processing sensory information can lead to deafferentation, or the “release phenomenon.” This occurs when input to a sensory area is lost, causing remaining neurons to become spontaneously hyperactive and generate their own signals, thereby creating the hallucination.
Damage to the occipital lobe, located at the back of the head, is most frequently implicated in visual hallucinations because it houses the primary visual cortex. When a stroke impacts this region, the brain generates images to fill the void created by the loss of visual input. The complexity of the hallucination, from simple geometric shapes to detailed scenes, relates to whether the damage affects the primary visual cortex or higher-order visual association areas.
The thalamus, a central relay station for sensory and motor signals, also plays a significant role when damaged. A stroke in the thalamus or midbrain can lead to peduncular hallucinosis, characterized by vivid, colorful, and non-threatening visual hallucinations. Since the thalamus filters and redirects information before it reaches the cerebral cortex, its injury results in a failure to regulate sensory flow, causing misperceptions.
Injury to the parietal lobe, which processes touch, spatial orientation, and body awareness, can result in tactile and somatic hallucinations. This damage disrupts the brain’s map of the body, leading to false sensations of movement or touch, such as the feeling that a paralyzed limb is still moving.
Differentiating Hallucinations from Delirium and Other Post-Stroke Symptoms
It is important to distinguish true hallucinations, which are focused sensory experiences, from other forms of post-stroke cognitive impairment, especially delirium. Delirium is a state of acute confusion and altered consciousness that is common after a stroke, affecting approximately one in four patients. Unlike a hallucination, delirium involves a global disturbance in attention, awareness, and cognition, with symptoms that fluctuate throughout the day.
While hallucinations can occur within delirium, the two are clinically distinct; delirium also involves disorientation and disorganized thinking. Clinicians must also rule out medication side effects. Certain drugs used in post-stroke care, such as some pain relievers or anti-seizure medications, can cause temporary alterations in perception that mimic true hallucinations.
Psychotic symptoms related to the stroke must be separated from pre-existing or new-onset psychiatric conditions. True post-stroke hallucinations are a direct result of the brain lesion, whereas conditions like psychosis have different underlying mechanisms. The precise location of the brain injury, the patient’s level of insight, and the presence of fluctuating attention help medical professionals make an accurate diagnosis.