Petit mal seizures in adults result from abnormal electrical signaling between the thalamus and cortex, two brain regions that normally work together to regulate consciousness and attention. These seizures, now formally called absence seizures, cause a brief lapse in awareness lasting 5 to 30 seconds, often with a blank stare and rapid eye blinking. In adults, they can stem from childhood epilepsy that never fully resolved, new-onset genetic epilepsy, or triggers that unmask an underlying vulnerability in brain circuitry.
How the Brain Produces an Absence Seizure
Your brain maintains a careful balance between excitatory signals (which activate neurons) and inhibitory signals (which quiet them down). Absence seizures happen when this balance tips toward excessive excitation in a specific loop connecting the cortex and thalamus. Neurons in a part of the thalamus called the reticular nucleus normally send inhibitory signals to relay centers deeper in the thalamus, creating a braking system known as feed-forward inhibition. When that braking system weakens or fails, neurons across both regions begin firing in lockstep, producing the characteristic 2 to 4 Hz spike-and-wave discharges visible on an EEG.
This hypersynchronous firing is what causes the sudden “blank out.” Because the thalamocortical loop is involved in maintaining awareness, its disruption temporarily disconnects a person from their surroundings without causing a full convulsive seizure. The episode typically ends as abruptly as it starts, with the person resuming whatever they were doing, often unaware anything happened.
Genetic and Hereditary Causes
Most absence seizures have a genetic component. The mutations most commonly identified affect ion channels and a signaling system that uses a brain chemical called GABA, which is the brain’s primary inhibitory messenger. Specific genes linked to absence seizures include GABRG2, SLC6A1, CACNB4, and SCN8A, all of which influence how neurons regulate their own excitability. When these genes carry harmful variants, the feed-forward inhibition in the thalamocortical loop becomes less effective, making synchronized misfiring more likely.
Absence epilepsy often runs in families, though the inheritance pattern is complex. Rather than a single gene causing the condition outright, multiple genetic variants typically combine to raise a person’s threshold for seizures. This is why two siblings with similar genetics might have very different seizure histories.
Why Absence Seizures Appear or Persist in Adults
Absence seizures are far more common in children, so when they occur in adults, the explanation usually falls into one of three categories.
The most common scenario is childhood absence epilepsy that was never fully outgrown. Remission rates for childhood absence epilepsy range from 56% to 84%, meaning a significant minority of people continue having seizures into adulthood. Among those who do achieve remission and stop medication, roughly 17% experience seizure recurrence and need to resume treatment. Juvenile absence epilepsy, which begins in the early teen years, has even lower remission rates (37% to 62%) and is more likely to persist as a lifelong condition.
Less commonly, adults develop new-onset absence seizures without a clear childhood history. This can happen when an underlying genetic predisposition is unmasked by physiological stress, hormonal changes, or other factors that shift the brain’s excitation-inhibition balance. New-onset absence seizures in adults also warrant careful evaluation because what looks like an absence seizure can sometimes turn out to be a different seizure type entirely.
Triggers That Provoke Episodes
Even in someone with an underlying predisposition, specific triggers can increase the frequency of absence seizures. Sleep deprivation is one of the most reliable. When the brain is under-rested, its inhibitory systems function less efficiently, lowering the threshold for the thalamocortical loop to misfire.
Hyperventilation is such a potent trigger that neurologists deliberately use it during EEG testing. Rapid, deep breathing for several minutes changes blood chemistry in ways that make absence seizure patterns easier to provoke and detect. Flickering or flashing lights can also trigger episodes in people with photosensitivity. Stress, alcohol use, and missed doses of seizure medication are additional common triggers in adults.
How Absence Seizures Differ From Other Lapses
In adults, absence seizures are frequently misdiagnosed or mistaken for a different seizure type called focal impaired awareness seizures (previously known as complex partial seizures). The distinction matters because the two have different causes, different brain regions involved, and different treatment approaches.
True absence seizures typically last under 30 seconds, start and stop abruptly, and involve minimal movement beyond a blank stare, rapid blinking, or subtle chewing motions. The person returns to full awareness almost instantly. Focal impaired awareness seizures tend to last longer (one to two minutes), involve more noticeable automatic behaviors like lip smacking, picking at clothes, or wandering, and are followed by a period of confusion or disorientation. An EEG showing the bilateral 2 to 4 Hz spike-and-wave pattern confirms a true absence seizure, while focal seizures produce electrical abnormalities localized to one brain region.
Mental Health and Cognitive Effects
Adults living with ongoing absence seizures often deal with more than the seizures themselves. About 35% of people with epilepsy have at least one psychiatric condition. Anxiety disorders are the most common, affecting roughly 23% of people with epilepsy, followed by mood disorders like depression at 15%. Substance use issues and personality disorders each occur in about 7%, and psychosis in around 3%.
These rates are substantially higher than in the general population, and the relationship runs in both directions. The same thalamocortical circuitry involved in absence seizures plays a role in attention, mood regulation, and cognitive processing. Frequent absence seizures, even brief ones, can fragment attention and interfere with memory consolidation over time. Adults who have had absence seizures since childhood sometimes describe a lifelong pattern of difficulty sustaining focus, which may have been attributed to ADHD or inattentiveness before the seizures were identified.