The seizure threshold is the minimum level of abnormal electrical activity required to trigger a clinical seizure. Everyone has a threshold, determined by the balance between excitatory and inhibitory forces in the central nervous system. A lower threshold means the brain is more susceptible to sudden, disorganized electrical discharges, increasing the likelihood of a seizure. While conditions like epilepsy cause a chronically low threshold, susceptibility can fluctuate based on various internal and external factors. Understanding these common triggers is crucial for managing seizure risk, as they temporarily disrupt the brain’s stable electrical environment.
Daily Physiological Factors
Sleep deprivation significantly lowers the seizure threshold by increasing cortical excitability. Lack of adequate rest disrupts the brain’s normal electrical rhythms and reduces inhibitory processes. Neurologists sometimes use sleep deprivation to provoke epileptiform activity during an electroencephalogram (EEG) for diagnostic purposes.
Acute stress and anxiety contribute to neuronal instability through the release of stress hormones. Cortisol, a primary stress hormone, increases neuronal excitability, particularly in limbic structures. This hormonal hypersecretion alters the modulation of GABA receptors, which are responsible for inhibitory signaling.
Systemic illness, especially when accompanied by a high fever, can temporarily reduce the seizure threshold. Fever (hyperthermia) increases neuronal excitability, but inflammation is also a significant mechanism. Pro-inflammatory cytokines released during infection directly impact the central nervous system, creating an imbalance between excitatory and inhibitory neurotransmission.
Medications and Recreational Substances
Exogenous chemicals can interfere with neurotransmitter balance, making the brain more susceptible to seizures. Certain non-epilepsy medications possess pro-convulsant properties by acting on the central nervous system. For example, the antidepressant Bupropion lowers the threshold in a dose-dependent manner due to its effects on excitatory signaling.
Other medications that lower the threshold include certain antibiotics, such as fluoroquinolones, which diminish inhibitory signaling by antagonizing GABA-A receptors. Specific high-dose antihistamines and the atypical opioid Tramadol also increase seizure susceptibility. Individuals should discuss all prescription and over-the-counter drugs with their neurologist to assess potential risks.
Alcohol consumption presents a complex, biphasic risk to the seizure threshold. While immediate consumption may not trigger a seizure, the most significant risk occurs during acute withdrawal. The brain adapts to alcohol’s depressant effect by increasing its own excitability, leading to rebound hyperexcitability when the substance is cleared. Stimulant illicit drugs, such as cocaine and amphetamines, drastically increase neuronal firing rates by enhancing monoaminergic activity, making a seizure more likely.
Internal Chemical Imbalances
The brain requires a regulated chemical environment to maintain stable neuronal function; disruptions can lower the seizure threshold. Hypoglycemia (low blood sugar) is a significant metabolic trigger because the brain relies almost exclusively on glucose for energy. Insufficient glucose starves neurons, making them unstable and prone to misfiring, often due to missed meals or aggressive diabetes management.
Electrolyte disturbances are destabilizing because ions like sodium, potassium, calcium, and magnesium are critical for regulating action potentials. Hyponatremia (low sodium), hypocalcemia, and hypomagnesemia all contribute to neuronal hyperexcitability. These imbalances disrupt the electrical gradient needed for normal communication.
Severe dehydration often contributes to these electrolyte imbalances by concentrating body fluids and disrupting ion ratios. Dehydration also reduces blood volume, which can impact cerebral blood flow and the brain’s ability to function stably. Maintaining appropriate fluid and nutrient intake is a protective measure against lowering the threshold.
Sensory and Environmental Stimuli
External factors that overload sensory processing systems can provoke a seizure by overwhelming the brain’s ability to cope. Photosensitivity is the most well-known sensory trigger, involving specific visual stimuli. These stimuli often include flashing or flickering lights, geometric patterns, or rapid visual changes found in some video games. The flickering light causes neurons in the visual cortex to fire synchronously, which can then spread to other brain regions.
Extreme environmental conditions, particularly overheating, can also stress the central nervous system and lower the threshold. Hyperthermia, whether from strenuous exercise or hot weather, strains the body’s homeostatic mechanisms. This systemic stress can lead to physiological changes, including fluid and electrolyte loss, contributing to increased neuronal vulnerability.