The deep telencephalic regions have roles in movement control, emotions, and learning & memory. The movement control portion is composed of the basal ganglia. The emotion portion is due to a number of brain regions including the amygdala and is referred to as our limbic system. Learning and memory also takes place across the entire brain, but seems to be established in part through the hippocampus . These regions are the focus of this web page.
Note that the term basal ganglia is plural ("ganglion" is singular, "ganglia" is plural). That is because there are a number of gray matter regions that are all interconnected that make up the basal ganglia. These regions are:
The substantia nigra in the midbrain (and some also add the amygdala here, too) work with those three basal ganglia regions to help coordinate planned movements. This may seem to be the same function as the other motor regions, but it is not exactly the same. The best way to understand that is by telling you that in Parkinson's disease, the basal ganglia are severely affected, and the motor deficits are different from the motor deficits in cerebellar lesion.
In Parkinson's disease, an affected person has difficulties maintaining movements and in not tensing up. So, a severely affected person might be walking along and get stuck; they step right and left a bit and then suddenly cannot bring their next foot forward, so they are literally stuck in position. The way around that is to provide them with a novel setting, like by putting something in front of their stuck foot so that they can step over it. You may also know about the tendency for someone with Parkinson's disease to tense up-- you may have seen the characteristic Parkinson's tremor of the hands. Basically, the severely affected person has problems with hand shaking whenever they are not using their hands. This is a condition that gets worse with time, as the muscles in the Parkinson's patient continue to produce more and more force without reason. Eventually, if unmedicated, a Parkinson's patient could find themselves in a muscular contraction of antagonists that freezes them in position.
The importance of these deep telencephalic structures in movement control should now be apparent.
This telencephalic region is important in the limbic system. The limbic system is simply a number of brain regions that communicate with each other and help us produce emotions. The hypothalamus of the diencephalon is also important in this system. Your book also includes the hippocampus in the limbic system. We learned that the cingulate gyrus is also very important in emotions, although it is cortical and not deep. The amygdala, though, is a deep telencephalic structure and has its main role in emotions... none of the other deep telencephalic regions can be said to have a main role in emotions.
The amygdala is a large clump of gray matter on each side of the brain that is interconnected with many other regions of gray matter in the brain. As you are well aware, our emotions are complex. We respond emotionally to many different situations in many different ways. That requires a lot of input to the brain and a lot of processing of this input. That's why so many brain regions are involved. The amygdala is just one of the important brain regions involved. It is also highly connected with our learning and memory systems. That should make sense to you, since emotions and memory are certainly related to one another in life.
The hippocampus is a C-shaped region of the deep telencephalon, found on both sides of the brain. It's shape should make more sense after our second week of brain dissections in lab. The hippocampus is thought to be extremely important in establishing new memories and in learning new material.
An Alzheimer's patient has a difficult time learning new things. In fact, as the disease worsens, the patient cannot remember recent events, but can only remember events that happened a long time before. When one looks at the brain of a patient who died with Alzheimer's disease, one sees that the cells of the hippocampus are severely affected. This makes sense, because the hippocampus helps create new memories, and without a well-functioning hippocampus, an Alzheimer's patient cannot do this.
But memories do not reside within the hippocampus, they are just created there. Somehow, after memories are created, they become resident throughout the cerebrum. Our learning is also distributed throughout the cerebrum. The amygdala may also have a role in some portions of learning and memory.
From work that began on sea slugs, we have learned that the way we learn new things and establish new memories is by fine-tuning synaptic connections. Our brain makes new synapses and removes old synapses all the time, to create new pathways of interconnections within the brain. These new pathways are our new ideas and memories. These are difficult to resolve under the microscope, so much work continues toward understanding how our brains are actually working to make us new memories. But, for our discussion at this time, an understanding that the hippocampus has a role in the establishment of new connections, and then the rest of the telencephalon gets involved in housing the new memories, is enough.
© 2011 STCC Foundation Press