Epilepsy And Brain Regions
Charles Ribak, Ph.D. (Professor of Anatomy and Neurobiology, UC Irvine School of Medicine) gives expert video advice on: What is the "cerebellum" and how does it factor into epilepsy?; What is the "frontal lobe" and how does it factor into epilepsy? and more...
What is the "amygdala" and how does it factor into epilepsy?
There are many parts of the brain and the amygdala is one of the structures located in the temporal lobe of the brain. Temporal lobe epilepsy is an entire category of epilepsy, and the amygdala takes up a large part of this portion of the brain. The amygdala is deep to the temporal cortex, and it relates a lot with other structures that are part of the limbic system. The limbic is our emotional brain. It involves our emotions: getting angry, being happy, etc. This is what the amygdala is involved in. There are many other functions, but, for the most part, I think that simplifies what the amygdala is all about.
What is the "cerebellum" and how does it factor into epilepsy?
The cerebellum is a portion of the brain that is mainly connected with the brain stem, and it's involved in motor coordination. The seizures that most people have are motor seizures, and so the cerebellum would become activated during this period of time of the seizure, but it's not considered to be the source of the epileptic focus in most cases.
What is the "cerebral cortex"?
The cerebral cortex is a six-layered neuronal structure that is on the outside portion of the entire forebrain. So, on the cerebral hemisphere, the entire outside is the cerebral cortex. It's a six-layered structure, and it is broken into four lobes. We talk about four different lobes, and we utilise the four main cranial bones that overlie the cortex to define those regions. So, we have a frontal bone, and behind the frontal bone is frontal cortex; the frontal cerebral cortex. The temporal bone, just above the ears. We have, just beneath that, aligned deep to that, is the temporal cortex. Then, we have our parietal cortex that's above it. This region is involved in sensory perception. Last, but not least, is the hardest part of your cranium; the part that if you fall backwards you hit your head on is your occipital bone. Right underneath the occipital bone is occipital cortex. Most of the occipital cortex deals with the function of vision.
What is the "frontal lobe" and how does it factor into epilepsy?
The frontal lobe underlies the frontal bone, and it is a large part of cerebral cortex that also contains the motor cortex which is a strip that goes from the medial aspect of the frontal lobe all the way down to the sylvian fissure where the temporal lobe begins, and this motor strip controls the musculature for the contralateral body. Now, in seizures that start in the motor cortex, there can be a very restrictive focus. For example you could have a little brain tumor growing in the part of the motor cortex that controls the fingers on the hand contralateral to it, and if that's the case, if the seizure starts there, you may see uncontrollable movement of that hand, and then as the seizure generalizes, in other words as more neurons in the motor cortex become recruited into this synchronized bursting activity, you could have the entire arm moving and shaking, as well as spreading down to the leg on that same side. And then it could also cross the corpus callosum and then get the other side of the brain involved, as well as the other side of the body involved, in that motor seizure.
What is the "temporal lobe" and how does it factor into epilepsy?
The temporal lobe is part of the cerebral cortex found just below the temporal bone. Now, the temporal bone is one of the thinnest of the skull bones, and the temporal lobe consists of areas that are specialized for hearing—this is on the lateral surface, the auditory cortex. And then we also have, as I mentioned to you earlier, structures that are involved in temporal lobe epilepsy. And these are found on the medial portion of the temporal lobe. These are the so-called mesial temporal structures. These include the hippocampus and the amygdala. A different kind of seizure starts from these regions because these regions are involved in the emotional part of the brain known as the “limbic cortex,” or the “limbic system.” And so these seizures are oftentimes referred to as “complex partial seizures.”
What is the "hippocampus" and how does it factor into epilepsy?
The hippocampus is a structure found in the medial portion of the temporal lobe. It functions, normally, in learning and memory. Also, it's involved in spatial orientation, so when you're trying to locate the nearest McDonald's, you can more or less orient yourself, and you know where to make a right-hand turn, drive a few more blocks, make a left-hand turn, and there's your store. So this is all part of the function, the normal function, of the hippocampus.Now the hippocampus is set up in such a way that it has a lot of connections with other temporal structures, and also these structures have connections with other parts of the cerebral cortex. So if there is a burst of activity, a synchronized bursting of activity, of neurons in the hippocampus, this can lead to a seizure as well.
What is the "vagus nerve"?
With epilepsy, the vagus nerve is one of the 12 cranial nerves, it is Roman numeral 1. The vagus nerve has the longest extent, arising from the cranium (coming from the brain stem); it distributes through the neck, through the upper thorax, all the way down into the abdomen. The vagus nerve even gets into the stomach and maybe a little bit of the gut. The vagus nerve is involved in regulating our heartbeat, sensing when our stomach is upset, and also when our heart is beating too fast. So, it is part of our autonomic nervous system, and relays its information into the brain stem into a certain defined nucleus, called the solitary nucleus (mainly because it sits there all by itself). This nucleus has very vast projections to various autonomic centers of the brain that regulate heartbeat, thirst, hunger, mainly the hypothalamus, but also other limbic structures.