What is a seizure?
Over-activity in the brain can cause a variety of responses in the body which are medically categorized as different types of seizures. The video and video notes below describe seizures on the organ (brain) level and cellular (neuronal) level.
On the organism level, seizures can range from the afflicted individual seeming to space out during an absence seizure to the full-body convulstants of tonic-clonic seizures. Absence seizures are also called petit mal seizures and tonic-clonic seizures are also called grand mal seizures.
The video above shows what occurs in the brain during a seizure. As the video is silent, below is an explanation of what we see in the clip:
0:15 – The video focuses on a synapse or structure where communication between neurons occurs One neuron extends and reaches out towards, but not quite touching, another neuron’s extension. In the video, red and blue-purple spheres represent neurotransmitters, or chemicals that neurons use to communicate with each other. The neurotransmitters leave the neuron on top and carry information to the neuron below.
0:20 – In the foreground, notice the how many neurotransmitters (little spheres in the video) are leaving the first (top) neuron to pass information to the second (bottom) neuron. Also take note of the rate of the background “flashes.” The flashes represent communication between neurons in the background. Both the neurotransmitter quantity and the rate of the flashes represent neuronal activity.
0:35-0:50 – Now, notice the rate of communication and activity in the foreground neuron and background neurons. The activity is increasing dramatically. We can see an “electric storm” of activity in the background. Scientists often use the metaphor of a lightning or electric storm to describe the abnormally high brain activity during a seizure.
0:50-0:58 – As the video zooms out, we see the that the increased activity has spread to the whole highlighted (orange) brain structure, the hippocampus.
1:02 – Now we see the brain structure pulse with activity. The over-activity begins to spread in the same side of the brain, or hemisphere, and then it spreads to the other hemisphere until it the majority of the brain is pulsing. This means that the seizure is spreading to other parts of the brain.
How are seizures connected to neurogenesis?
Seizure episodes impact neurogenesis. Seizures can increase the rate of neurogenesis in the dentate gyrus of the hippocampus. In rats, during this time of rapid neurogenesis, the progenitor cells have a decreased cell cycle length (Varodayan et al, 2009).
Factors that hamper neurogenesis can also increase the occurrence of epilepsy. For example, low levels of proteins, such as reelin, result in reduced neurogenesis rates. Specifically, in mice with insufficient reelin, the neurons do not migrate to the appropriate layers. Epilepsy can also result from such deficiencies (Haas et al, 2010).
Seizure pharmaceuticals can impact neurogenesis. Valproic acid (VPA), an anti-epilepsy medicine, can also block the increased neurogenesis. The VPA-protected mice maintained normal cognitive function following the seizure and learned as well as normal rats (Jessberger et al, 2007).
For additional information about seizures:
Video about seizure disorders:
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Website about seizure disorders: http://www.epilepsyfoundation.org
Page by Chelsea Michael