Forebrain: Definition & Function

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Sarah Phenix
Expert Contributor
Ana Benito Gonzalez

Ana has a PhD in Biology. She has taught college classes at leading U.S. universities, also works as a Biology tutor. She has published several scientific journals.

The forebrain is the recently developed part of the brain. Explore the definition and function of the forebrain and learn about the external and internal structures of the forebrain and the four main lobes into which it is divided. Updated: 11/22/2021

What Is the Forebrain?

Have you ever heard the term 'reptilian brain' used to describe the human brain? This refers to the primal part of our brain that we actually share structurally with a reptile's brain. Reptiles are, evolutionarily speaking, one of the oldest living organisms; therefore, our 'reptilian brain' is the developmentally oldest portion of the brain, while the forebrain is the most recent. Let's explore this massively advanced, yet evolutionarily young, portion of our supercomputer human brain.

Three regions of the brain

The term forebrain means 'last brain,' or the most recently developed portion of our brain. It controls everything from voluntary movement and the integration of sensory information to all our higher abstract thought, logic, speech, and emotions. Basically, the development of the forebrain is why we humans are so intellectually advanced. Let's look at the structures of the forebrain that enable our cognitive abilities.

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  • 0:00 What Is the Forebrain?
  • 0:54 External Structures
  • 2:50 Internal Structures
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External Structures

Superficial structures of the forebrain
Superficial Structures of the Forebrain

The most obvious structure of the forebrain is the cerebrum, which is divided into a left and right hemisphere by a deep groove called the longitudinal fissure. The right hemisphere is our artistic and creative side, while the left hemisphere is our logical, recollecting side for facts and figures. Generally speaking, the cerebrum is the tissue that most people think of as 'brain tissue' as it is the largest portion of our brain. Let's take a moment to explore the superficial structures of the cerebrum before jumping into the deep structures.

Have you ever watched a TV show where the doctors spoke about the 'gray matter' and 'white matter' of the brain? Well, both of these tissue types are part of the cerebrum; gray matter is cortex tissue (outer tissue), while white matter is deep tissue (inner tissue) below gray matter. White matter is composed of neurons encased in a fatty white sheath called myelin. This insulates the neurons, aiding in rapid transit of neural signals. gray matter is unmyelinated (without myelin) and so appears gray.

The cerebrum is said to look something like a walnut and has some very unique external features other than its two hemispheres. The cerebrum has many little folds of tissues called gyres. The gyres have depressions between them called sulci (plural for sulcus). These folds and depressions increase cortical surface area. More cortical tissue equals more neurons to transmit thought, emotion, and muscle control signals. Did you know that if you were to smooth out all of the gray matter of your brain, it would be anywhere from 233 to 465 square inches or one to two full-sized sheets of newspaper?

Lobes of the brain
Lobes of the Brain

The cerebrum is divided into four main lobes:

  • The frontal lobe
  • Temporal lobe
  • Parietal lobe
  • And the occipital lobe

Internal Structures

The cerebral cortex is the outermost layer of the brain. Deep in the cerebral cortex, nestled in the white matter of the cerebrum are three main structures of the forebrain called:

  • The thalamus
  • Hypothalamus
  • And the limbic system

Let's explore where each of these are as well as what they do.

Deep structures of the forebrain
Deep structures of the Forebrain

The thalami (plural of thalamus) are two egg-shaped structures that sit deep in the cerebrum. It is an important structure as the main relay station between the sensory impulses that come from the environment and go to your brain. You can think of the thalamus like the UPS man who ensures that 'packages,' in this case sensory impulses such as touch, pain, or equilibrium, are received at the correct 'address' in your brain. Without the thalamus sorting our neural signals, the world might become a really confusing place. For instance, receiving sensations regarding pain in our hand in the area of our brain meant for interpreting sight would be quite the mix-up.

The hypothalamus is so named as it is 'hypo' (below) the thalamus. It's a cone-shaped structure that unites your autonomic nervous system with your endocrine system. The endocrine system of your body is responsible for hormone secretion into your blood stream. Its endocrine role is due to the pituitary gland, which is connected to the cerebrum via the tip of the hypothalamic cone. Therefore, it relays information to and from the cerebrum and the hormone secreting pituitary gland. As such, the hypothalamus controls responses such as thirst, hunger, fatigue, sleep patterns, and body temperature.

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Additional Activities

The Forebrain

The Cortex

The most external part of the forebrain, the cortex, is divided into four main lobes. In order to understand the brain a little bit better you should know that each one of these lobes in the forebrain is associated with different functions. Review what are the main functions of each lobe and answer the following questions:

  1. Which lobe will be the most likely damaged if a person has suffered from changes in personality?
  2. Which lobe will be the most likely damaged if a person has trouble seeing?
  3. Which lobe will be the most likely damaged if a person had trouble finding the right words when speaking?
  4. Which lobe will be the most likely damaged if a person has trouble hearing?


  1. The frontal lobe.
  2. The occipital lobe.
  3. The temporal lobe.
  4. The temporal lobe as well.

Internal Structures

The forebrain is also made up of several internal structures. Each of these parts has very specific roles as well. Try to determine what would happen if any of these areas were compromised by some kind of brain injury.

  1. What would happen to an individual if their hypothalamus were damaged? What functions might be compromised?
  2. What would happen to an individual if their limbic system were damaged? What functions might be compromised?
  3. What would happen to an individual if their thalamus were damaged? What functions might be compromised?
  4. Which of those three structures do you think will be the most important for an individual, in terms of survival?


  1. The hypothalamus is responsible for releasing hormones and regulating body temperature for example.
  2. The limbic system is responsible for regulating emotions, such as fear and anxiety.
  3. The thalamus is the main relay system between the body and the brain, which means that most pathways stop there when going in and out of the brain. Many vital functions could be compromised if damaged.
  4. The thalamus would be the most critical structure for survival. Its damage could lead to motor and sensory issues, but it could also have more severe consequences such as inducing a permanent coma (state of unconsciousness).

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