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Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics
in 2 minutes or less.
In this installment I will discuss epilepsy.
Epilepsy is a chronic condition that is characterized by recurrent seizures; seizures are temporary
disruptions of normal brain activity caused by excessive neural activity.
Epilepsy can have genetic and acquired causes, but in most cases the cause is not known.
Seizures can look drastically different depending on the patient, ranging from a brief and subtle
interruption in consciousness to violent convulsions.
One characteristic seizures have in common, however, is excessive neural activity.
In a healthy brain, different groups of neurons are all firing action potentials at different
times.
During a seizure, however, firing rates are increased and groups of neurons all fire at
the same time, leading to large spikes in neural activity.
In seizures called focal seizures, this excessive activity begins in one specific area of the
brain called the seizure focus, but it can also propagate to other areas of the brain.
Neurons that are in the seizure focus experience a large and long-lasting depolarization followed
by the firing of a train of action potentials.
This abnormal activity is referred to as a paroxysmal depolarizing shift.
The unusual activity is normally confined to the area it originated in, but during a
seizure it can spread due to the failure of inhibitory mechanisms, leading to widespread
abnormalities in brain function.
In seizures called generalized seizures, excessive activity seems to arise in widespread areas
of the brain all at once.
Although the mechanisms underlying this are not fully understood, generalized seizures
may involve a pervasive hyperexcitability of neurons throughout the cortex along with
abnormalities in neural networks that connect the thalamus to the cortex.