What Are the Parts of the Brain and Their Functions?

The brain is divided into three (3) major regions - the hindbrain, the midbrain and the forebrain. Each region is composed of different brain parts that work together to process the information they receive.

Hindbrain

The Hindbrain is located at the rear of the skull and is the lowest portion of the brain. Hindbrain parts include the medulla, the cerebellum and the pons.

The medulla is where the spinal cord enters the skull. It is responsible for controlling breathing, regulating reflexes, and maintaining an upright posture of the body.
The cerebellum are two (2) rounded structures located besides the medulla. It is responsible for coordinating motor activity (movements of the body), so that extensive damage of the cerebellum can cause failure to even stand up.
The pons serves as the bridge towards the midbrain. It is a cluster of neuronal fibers surrounding the reticular formation (discussed below), and is responsible for monitoring sleep and arousal by coordinating with the autonomic nervous system.

The Brain Stem evolved 500 million years ago and is the most ancient part of the brain. It is composed of the hindbrain, plus the midbrain, minus the cerebellum. It is involved in alertness and in monitoring basic survival functions such as breathing, heartbeat, and blood pressure. It is also known as the "reptilian brain" because it is considered the entire brain of reptiles.

Midbrain

The Midbrain serves to relay information between the hindbrain and the forebrain, particularly information coming from the eyes and the ears. It is composed of two (2) systems - the reticular formation, and a cluster of neurons having dopamine, serotonin and norepinephrine receptors.

The reticular formation is involved with stereotypical patterns of behavior such as walking, sleeping, and other reflexes. Parkinson's disease, a degenerative disease of the brain that causes involuntary tremors on affected body parts, damages a section near the bottom of the midbrain.

Forebrain

The Forebrain is considered as the highest region of the brain because it essentially differentiates us humans from the rest in the animal kingdom. This region is also involved in processing complex information. (The midbrain and hindbrain are similar with other animals, hence the term Brain Stem.) The forebrain is composed of the limbic system, the thalamus, the hypothalamus, the basal ganglia, and the cerebral cortex.

The limbic system is made up of the amygdala and the hippocampus. From a Latin word meaning "almond", owing to its shape, the amygdala is responsible for processing emotions - how humans become aware of them and how we express them. It is also critical for our survival because it helps us discriminate one object from another. For instance, damage of the amygdala may cause us humans to eat our own feces, fight the wrong "enemy", or try to mate with a chair. The hippocampus, on the other hand, is presumably involved in memory storage because damage to the part actually results to inability to store new information. Patients with damaged hippocampus therefore live the day without remembering yesterday. Overall, the limbic system is involved in memories and emotions by determining which neuronal connections should be strengthened and which should be rewired.
The thalamus sits on top of the brain stem. It sorts and relays incoming information to the different parts of the forebrain. For example, information coming from the cerebellum is oftentimes relayed to the motor cortex in the cerebral cortex (discussed below). The thalamus also works with the reticular formation on regulating states of sleep and wakefulness.
The hypothalamus is located just below the thalamus, hence the name. It monitors pleasurable activities such as eating, drinking and sex. It influences the endocrine system, particularly the pituitary gland, in secreting hormones in response to different emotions, stress and rewarding feelings.
The basal ganglia is a cluster of neurons sandwiched between the thalamus and the cerebral cortex. It works with the cerebral cortex and the cerebellum for coordinating voluntary movements, particularly in forming habitual behaviors, such as bicycle riding and typing. Just like the bottom section of the midbrain, the basal ganglia gets damaged with Parkinson's Disease. This is the reason why Parkinson's patients oftentimes produce slow and unwanted movements.
The cerebral cortex is the most recently developed (or evolved) part of the brain. Like a crumpled paper, it almost completely caps the rest of the brain parts. It is also the largest part of the human brain, making up to 80% of the brain's volume. High-level processing also takes place in this part of the brain. Because of the complexity and the influence of the cerebral cortex in various behaviors and mental processes, this part of the brain deserves to be treated more in-depth below.

Cerebral Cortex

Hemispheric Division

The cerebral cortex is divided into two (2) hemispheres - the left and the right hemispheres. The left hemisphere is associated with verbal processing, such as speech and grammar, and mathematics; while the right hemisphere is involved with nonverbal processing, such as spatial perception, visual recognition and emotion. The left hemisphere processes information coming from the right side of the body, while the right hemisphere processes information coming from the left side of the body. The two hemispheres of the brain are connected with each other by a bundle of axons called the corpus callosum. This connection allows the left and the right hemispheres to communicate and integrate information with each other.

Two notable areas in the left hemisphere are the Broca's and Wernicke's areas. The Broca's area was discovered in 1861 by a French surgeon named Paul Broca, when he evaluated a man called Tan. Tan was named so because "tan" was the only word he could speak. His condition is known as aphasia. Tan's autopsy revealed that his brain was damaged in a certain area in the left hemisphere. Broca's area turned out to be involved with speech production, while Wernicke's area is significant for language comprehension.

Roger Sperry researched about the importance of the corpus callosum in integrating the information processed in the left and right hemispheres of the brain. In 1968, he examined W.J., whose corpus callosum was surgically severed. 6 years after (1972), he experimented with cats by cutting off their corpus callosums and some connections of their eyes to their brains. He found that cats needed to relearn what they saw from one eye when a visual task is moved to the other eye. Furthermore, he observed that logical thinking is predominantly centered on left brain activity, while creative activities are more associated with right brain activity. Sperry's study was known Split-Brain Research. As soon as the media found out about his studies, the results were sensationalized and reduced to casual left-right brain categorization. People began to typify themselves as either logical or creative/artistic. On a positive note, Sperry's research led to the realization that the school curricula needed to incorporate more creative and artistic activities for learning.

Cortices and Association Cortices

Aside from being divided into two hemispheres, the cerebral cortex is also divided into cortices and association cortices - visual, auditory, motor and sensory. Information coming from the environment are registered in the cortices and processed in the association cortices. Cortices may be mapped point to point. Wilder Penfield, a neurosurgeon from Montreal Neurological Institute, located where in the somato-sensory cortex and motor cortex several parts of the body are felt and moved. On the other hand, association cortices are integrative; they process the information received by the cortices. Because of this difference, damages to the cortices are based on location, while damages to the association cortices are based on their extent.

Cortical Lobes

The cerebral cortex is divided according to hemispheres, cortices, and association cortices. Lastly, it is also divided according to lobes - occipital, temporal, parietal and frontal.

The Occipital Lobe is located at the back of the head and is involved in processing visual information, such as color, shape and motion. Accordingly, the visual cortex and visual association cortex are located in this lobe. Damage to the occipital lobe may cause cross-eyeing and blindness partly or entirely of the visual field. Siamese cats, for example, are oftentimes born with defective visual cortex, so that they have to consciously cross their eyes just to see straight!
The Temporal Lobe is located just above the ears and is involved in hearing, language processing and memory (due to its connection with the limbic system). The auditory cortex, auditory association cortex, and part of the visual association cortex are located in this lobe. Damage to the temporal lobe leads to failure to store new information (just like damage to the hippocampus, as discussed above).
The Parietal Lobe is located at the top of the head and towards the rear. It is involved in attention and motor control, in processing spatial location, and in perceiving pain, touch and temperature. It is said that Albert Einstein's parietal lobe is 15% larger than average, probably the reason why he oftentimes imagined objects in space while formulating his theories. The sensory association cortex is located in this lobe.
The Frontal Lobe is located just behind the forehead and towards the top of the head. It constitutes 30% of the cerebral cortex in humans, 17% in chimps, 3.5% in cats, and it barely exists in rats. It is involved in the control of voluntary muscles, intelligence and personality. Its critical involvement with personality comes from the story of Phineas T. Gage, a 25-year old foreman whose personality was altered after an iron rod accidentally shot up and pierced his frontal lobe. From being mild-mannered, hardworking and emotionally calm, he became obstinate, moody, irresponsible and selfish. The most important portion of the frontal lobe is the prefrontal cortex. It is sometimes referred to as the executive control system of the body as it is involved in planning, reasoning, and monitoring and organizing thinking. Damage to the frontal lobe causes failure to follow basic directions, distraction from irrelevant stimuli, and personality change. The somato-sensory cortex and motor cortex are located in this lobe.