Brain basics 2

Parts of the brain

amygdala

The amygdala is part of the limbic system.

It is an almond-shaped structure located deep in the temporal lobe of the brain - indicated in orange in this diagram.

It is known to be involved in the processing of emotions such as fear, anger and pleasure.

It plays a role in emotional memory. It attaches emotional significance to information, and is responsible for determining what memories are stored and where the memories are stored in the brain, depending on the emotional response an event invokes.

It also mediates between aggressive and defensive behaviour.

caudate nucleus

The caudate nuclei are C-shaped structures located near the centre of the brain. There is a caudate nucleus in each hemishere.

The caudate is associated with learning and memory, the processing of feedback, and language comprehension.

It is believed to be dysfunctional in persons with OCD (obsessive compulsive behaviour).

cerebellum

In both these images, the frontal lobe is on the right, and the cerebellum is on the lower left.

Cerebellum is Latin for little brain. It is located near the brain stem, beneath the occipital lobes, at the base of the skull, at the back of the head. The compact folds and groves give it a ridged appearance and make it easily recognizable.

The cerebellum controls the coordination of learned, skilled movement, balance and equilibruim, and muscle tone.

cerebral cortex

Notice the dark outer layer in this image. That is the cerebral cortex, the outer layer of the the brain. The cortex is divided into the left and right brain hemispheres and appears wrinkled because it is compressed to fit into the skull.

The wrinkles or folds are called gyri (singular, gyrus).The valleys or infoldings are called sulci (singular, sulcus). Flattened out, the cortex would be roughly the size of an extra large pizza.

Believed to be the seat of the mind, the cerebral cortex is largely responsible for higher order brain functions, e.g., attention, emotions, memory, thought, language and consciousness.

cerebrum

The cerebrum - Latin for brain - is the largest part of the brain. It is divided into two hemispheres - the right and left hemispheres. The hemispheres of the brain are connected by a thick band of nerve fibers called the corpus callosum, which allows for communication between both hemispheres.

The outer area of the cerebrum is covered by a thin layer of cells - the cerebral cortex, which appears wrinkled because it is compressed to fit into the skull. The bulges are called gyri (singular gyrus), and the deep grooves are called sulci (singular sulcus).

The cerebrum is the most evolved part of the human brain and is responsible for higher order cognitive processes such as thinking, problem-solving, perceiving, and producing and understanding language.

cingulate gyrus

This MRI image shows the location of the cingulate gyrus, which lies immediately above the corpus callosum, the large bundle of nerves that connects the right and left brain hemispheres. The cingulate gyrus is part of the limbic system, which is involved with emotion, learning, and memory.

The cingulate gyrus is believed to play a role in linking behavioural outcomes to motivation - such as when a specific action produces a positive emotional response, and results in learning. It is believed the cingulate gyrus plays a role in the dysfunctional behaviour of persons with OCD (obsessive compulsive behaviour).

hippocampus

The hippocampus belongs to the limbic system. It is involved in the formation of new memories about experienced events and turns short-term to long-term memory. It is also associated with spatial orientation. There is one in each brain hemisphere.

In Alzheimer's disease, memory problems and disorientation appear among the early symptoms, because the hippocampus is one of the first areas of the brain to suffer damage.

The case of Henry Gustav Molaison, known until his death in 2008 as H.M., is well known.

After surgery that destroyed his hippocampus to relieve epileptic seizures, H.M. remembered his childhood, but could not remember events that occurred just before his surgery and was unable to form new memories.

hypothalamus

The hypothalamus belongs to the limbic system. It is located just above the brain stem and has many functions.

For example, it controls autonomic functions such as heart rate, digestion, and body temperature. It regulates food and water intake and the sleep-wake cycle.

The hypothalamus translates extreme emotions into physical responses.

nucleus basalis

The nucleus basalis is that part of the brain that helps us to focus our attention and remember what we are experiencing. It is a group of neurons in the lower area of the frontal lobe. During the critical period of early childhood, when learning is effortless, BDNF turns on the nucleus basalis, and keeps it turned on. After the main neuronal connections are in place, the brain releases BDNF in sufficient qualtities to turn off the nucleus basalis and end the critical period of effortless learning. From here on, the brain activates the nucleus basalis only when something new and interesting occurs, or when we make the effort to pay attention.

thalamus

Thalamus means "anteroom" - an area that leads to and connects to a main room. The thalamus receives auditory, somatosensory, and visual signals and relays them to the cortex. The thalamus is part of the limbic system.

vestibular apparatus - balance system

The vestibular apparatus is the sensory organ for the balance system. It gives us our sense of orientation in space. It detects motion of the head in space, which generates reflexes such as stabilizing our vision and maintaining head and body posture.

The image on the left shows the three canals that make up the vestibular system. They let us know when we are upright and how gravity is affecting our body by detecting movement in the horizontal plan, the vertical plan, and movement that is backward and forward.

Unlike seeing and hearng, we are usually unaware of the balance system when it is functioning normally.

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