The Forebrain (Learning Outcome 1)

The Forebrain (Learning Outcome 1)

• The forebrain is located rostrally (towards the nose) and has two main subdivisions:

•  the Telencephalon and the Diencephalon. .

Telencephalon

• Cerebrum = Left and right cerebral hemispheres, so the 2 hemisphere together make up the cerebrum

 

Cerebral hemispheres contain:

• Cerebral cortex - cortical , like the bark on a tree (outer layers )

• Limbic system - subcortical (beneath the cortex)

• Basal ganglia - subcortical (beneath the cortex)

Cerebral Cortex

The cerebral cortex surrounds the two cerebral hemispheres.

 

It is convoluted (folded) to increase overall surface area which helps with complex cognition.

 

Convolutions :

• sulci (small grooves (rillen))

• fissures (large grooves)

• gyri (bulges (ausbeulung) in between grooves)

 

When we learn about different structures and areas in the brain , we might reference to the different fissures and sulci, to help us identify where specific structures are in the brain

sulci

• sulci (small grooves (rillen))

fissures

• fissures (large grooves)

gyri

• gyri (bulges (ausbeulung) in between grooves)

Cerebral Cortex made up of :

Grey matter:

Named after it's colour, contains glia and lots of cell bodies which have a grey colour.

 

White matter:

Made up of glia and myelinated axons which have a white colour.

 

There are 4 lobes of the cerebral cortex:

1. Frontal (rostral to parietal lobe and dorsal to the temporal lobe)

2. Parietal (caudal to the frontal lobe and dorsal to the temporal lobe)

3. Temporal (rostral to the occipital lobe and ventral to parietal and frontal lobes)

4. Occipital (caudal to parietal and temporal lobes)

 

There are two of each lobe in the brain (one in each hemisphere)

Different parts of the cerebral cortex have different functions

Sensory Cortex: Three areas of the cerebral cortex receive information from sensory organs for processing

1. Primary visual cortex

1. Primary auditory cortex

1. Primary somatosensory cortex

1. Insular cortex

Primary visual cortex

• Located in the occipital lobe around the calcarine fissure (opening)

• Processes sensory information sent from the eyes

Primary auditory cortex

• Located in the temporal lobe near the lateral fissure

• Processes sensory information sent from the auditory system

Primary somatosensory cortex

• Located in the parietal lobe near the central sulcus

• Processes information sent from the somatosensory system (pressure - touch and pain)

Insular Cortex

the base of the somatosensory cortex and a portion of the insular cortex, which is normally hidden from view by the frontal and temporal lobes, receive information about taste.

• Helps to process taste information, alongside some functions from the somatosensory cortex

Primary Motor Cortex

• Movement control

• Located in the posterior part of the frontal lobe

Primary Motor Cortex (movement) and Primary

Somatosensory Cortex (pressure sensation )

Neurons in the different areas of each cortex are associated with different parts of the body

contralateral connections

For motor processing and all senses except taste and smell, the brain has contralateral connections

 

• Sensory information from the left goes to the right cerebral hemisphere

• Sensory information from the right goes to the left cerebral hemisphere

Member

Hemisphere

 

• Ipsilateral = same side ✅

• Contralateral = opposite side ❌

 

👉 Example:

 

• Left brain → right hand = contralateral

• Left brain → left hand = ipsilateral

🧠 Memory trick

👉 “Ipsi = identical side

The primary cortex only make up a small section of cerebral cortex

The primary cortex only make up a small section of cerebral cortex

 

Most of the cerebral cortex is made up of association cortex

 

• Association cortex help

accomplish everything between sensation and action , like planning, receiving

 

Eg visual association cortex , auditory association cortex …

central sulcus

The central sulcus provides ın important dividing line between the rostral and caudal regions of the cerebral cortex. (Look once more at Figure 3.9.) The rostral region is involved in movement-related activities, such as planning and executing behaviors. The caudal region is involved in perceiving and learning.

 

autotopagnosia, or "poor knowledge of one's own topography." The parietal lobes are involved with space: the right primarily with external space and the left with one's body and personal space.

autotopagnosia

poor knowledge of one's own topography." The parietal lobes are involved with space: the right primarily with external space and the left with one's body and personal space.

Sensory Association Cortex

• Each primary sensory area of the cerebral cortex sends information to adjacent sensory association cortex regions for further processing

• Eg Primary visual context sends information t the visual association cortex which is directly adjacent to it

• The regions of the sensory association cortex located closest to the primary sensory areas receive information from only one sensory system. For example, the region closest to the primary visual cortex analyzes visual information and stores visual memories.

• Regions further away receive information from more than one sensory system - allows us to connect information across senses

• Eg associating someone’s face with their voice

 

SimaoSensory Association Cortex damage

their deficits are related to somatosensation and to the environment in general. For example, they may have difficulty perceiving the shapes of objects that they can touch but not see, they may be unable to name parts of their bodies (see the following case of Mr. M.), or they may have trouble drawing maps or following them. Although people who sustain damage to the visual association cortex will not become blind, they may be unable to recognize objects by sight. People who sustain damage to the auditory association cortex may have difficulty perceiving speech or even producing meaningful speech of their own. People who sustain damage to regions of the association cortex at the junction of the three posterior lobes, where the somatosensory, visual, and auditory functions overlap, may have difficulty reading or writing.

 

Motor Association Cortex

• Sometimes called the premotor cortex

• Helps to control the primary motor cortex so movement

Prefrontal Cortex

Not directly involved in the control of movement, rather involved in planning and strategy (more complex processes )

Basal Ganglia

• Collection of nuclei below the cerebral cortex (subcortical) which lie beneath the anterior portion of the lateral ventricles.

 

• nuclei = an identifiable group of cell bodies in the CNS/ cell body that form a  structure  themselves

 

• Involved in motor control/ movement

 

The major parts of the basal ganglia are the caudate nucleus, the putamen, and the globus pallidus (the "nucleus with a tail," the "shell," and the "pale globe").

 

For example, Parkinson's disease is caused by the degeneration of certain neurons located in the midbrain that send axons to the caudate nucleus and the puta-men. The symptoms of this disease are weakness, tremors, rigidity of the limbs, poor balance, and difficulty in initiating movements.

 

🧠 Core idea first (don’t memorise randomly)

 

Think of the basal ganglia as a “movement gatekeeper”:

 

👉 It decides:

 

• ✅ what movements are allowed

• ❌ what movements are blocked

🔑 Easy memory trick

🚦 “Basal ganglia = Brain’s traffic lights”

 

• Green light → allow movement

• Red light → stop unwanted movement

So:

👉 Basal ganglia = smooth, controlled movement

Limbic System

• Widespread group of brain nuclei (group of cell bodies) that form a network

• Involved in learning, memory, and emotions

 

Among other structures, the limbic system, includes the

• limbic cortex, (limbus= meaning border ), ilcding an important region, the cingulate gyrus

• the amygdala (emotion processing),feelings and expressions of emotions, emotional memories, and recognition of the signs of emotions in other people.

•  and the hippocampus (learning and memory processes)

 

Besides the limbic cortex, the most important parts of the limbic system are the hippocampus ("seahorse") and the amygdala ("almond"), located next to the lateral ventricle in the temporal lobe. The for-nix ("arch") is a bundle of axons that connects the hippocampus with other regions of the brain, including the mammillary ("breast-shaped") bodies, protrusions on the base of the brain that contain parts of the hypothalamus.

🧠 Lateralization in the Cerebral Cortex

Definition

 

• Lateralization = some brain functions are mainly controlled by one hemisphere (left or right)

 

👉 The two hemispheres work together, but they are not identical

 

Left vs Right Hemisphere

🔹 Left Hemisphere (Analysis + Language)

 

• Specialised for analysis (breaking things into parts)

• Good at sequential / serial processing (step-by-step)

 

 

🗣 Key functions:

 

• Speech (talking)

• Understanding language

• Reading

• Writing

 

👉 Damage → problems with language (aphasia)

 

 

 

🔹 Right Hemisphere (Synthesis + Spatial)

 

• Specialised for synthesis (putting things together)

• Sees the big picture / whole

 

 

🎨 Key functions:

 

• Drawing (especially 3D)

• Spatial skills (maps, navigation)

• Recognising patterns and objects as a whole

• Constructing things

 

👉 Damage → problems with spatial awareness + visual organisation

 

 

 

🧠 Key Comparison (important!)

Left Hemisphere 🧠	Right Hemisphere 🧠
Analysis	Synthesis
Sequential	Holistic
Language	Spatial/visual
Verbal	Non-verbal

 

 

 

🔁 Important Note

 

• In some people, these functions can be reversed (rare

🔗 Connection Between Hemispheres

corpus callosum

 

• Large bundle of nerve fibres (axons)

• Connects left and right hemispheres

 

 

📌 Function:

 

• Allows communication between both sides

• Ensures:

  • Unified perception

  • Coordinated behaviour

 

👉 Without it, each hemisphere would process information separately

 

 

Lateralisation in the cerebral cortex

• The left hemisphere is more related to analysing information (extracting elements that make up an experience). This makes the left hemisphere well suited for processing serial events (things that happen in order) and controlling behaviour sequences. As you can imagine, this means that the left hemisphere is essential for language processing.  

 

• The right hemisphere is more related to the synthesis of information. This makes the right hemisphere good at combining things for holistic processing. This type of functionality is important for drawing and reading maps.

corpus callosum

• The corpus callosum is a large bundle of axons that interconnects corresponding regions of association cortex on each side of the brain. 

 

• For example, the left and right frontal lobes are connected, as are the left and right temporal, parietal, and occipital lobes. 

 

• The corpus callosum allows the two sides to talk to one another. Because of this, each part of the association cortex has an idea about what is happening in the corresponding region on the opposite side. 

 

 

The Diencephalon

Apart from the cerebral cortex, basal ganglia and limbic system of the Telencephalon, the other division of the forebrain, the Diencephalon contains two structures called the thalamus and hypothalamus.

 

The forebrain has two main divisions: the

telencephalon and the diencephalon

Diencephalon

The two most important parts of the diencephalon are the:

• Thalamus

• Hypothalamus

The Thalamus

Largest part of the diencephalon which sits above the hypothalamus (dorsal part of the diencephalon)

 

located near the middle of the cerebral hemispheres, immediately medial and caudal to the basal ganglia.

 

• Acts as a relay station/ send on and transmit information

 

• The nuclei (groups of cell bodies) have axons which are widespread throughout the cortex = important for sensory processing and motor control

 

The thalamus has two lobes, connected by a bridge of gray matter called the massa intermedia.

 

📥 Main function

• Most info going to cortex passes through the thalamus

👉 Think: “All roads go through the thalamus”

lateral geniculate nucleus

The Thalamus Contains the lateral geniculate nucleus which gets information from the eyes and sends it on to the primary visual cortex for detailed processing

 

3The eyes are processing sensory information form the left and right visual field and that formation is then send on to the LGN which then transmits the information to the primary visual cortex for further detailed processing

🧩 Types of thalamic nuclei

🔹 Sensory relay nuclei	🔹 Motor relay nuclei	🔹Association nuclei	🔹 Nonspecific nuclei
👉 Send sensory info → specific cortex areas   Examples:   LGN (lateral geniculate nucleus) → vision → visual cortex MGN (medial geniculate nucleus) → hearing → auditory cortex   👉 Memory: L = Light (vision) M = Music (hearing)	Send movement info → motor cortex   Example: Ventrolateral nucleus 👉 cerebellum → motor cortex	Relay info between cortical areas 👉 cortex ↔ thalamus ↔ cortex	Control overall brain activity (arousal/alertness) Project widely to entire cortex   👉 Think: “volume control of the brain”

The Hypothalamus

• Sits below the thalamus

The hypothalamus is situated on both sides of the ventral portion of the third ventricle. The hypothalamus is a complex structure, containing many nuclei and fiber tracts.

 

• Controls the endocrine system (hormones) and the autonomic nervous system (regulates bodily functions)

 

• Important for survival behaviours including reproduction, fighting and Eating, esca

 Hypothalamus and endocrine system

Note that the pituitary gland is attached to the base of the hypothalamus via the pituitary stalk.

Just in front of the pituitary stalk is the optic chiasm, where half of the axons in the optic nerves (from the eyes) cross from one side of the brain to the other.

 

 

The hypothalamus makes hormones which influence the endocrine system via connections with the pituitary gland

 

 

The pituitary gland has two parts:

anterior pituitary and posterior pituitary

 

Anterior Pituitary

 Blood vessels connect the hypothalamus and the anterior pituitary gland

 

• Neurosecretory cells of the hypothalamus release hormones which enter blood vessels and eventually cause the anterior pituitary gland to release its own hormones

 

• Many of these hormones control other endocrine glands (e.g., gonads) which release hormones that can influence brain and behaviour

 

For example, gonadotropin-releasing hormone causes the anterior pituitary gland to secrete the gonadotropic hormones, which play a role in reproductive physiology and behavior

 

Neurosecretory cells

Neurosecretory cells of the hypothalamus release hormones which enter blood vessels and eventually cause the anterior pituitary gland to release its own hormones

Posterior Pituitary

The posterior pituitary gland does not make its own hormones, while the anterior does

 

• Neurosecretory cells of the hypothalamus produce hormones which travel to the posterior pituitary gland via axoplasmic transport and are released via terminal buttons into the circulatory syste

 

• When these axons fire, the hormone contained within their terminal buttons is released and enters the circulatory system.

 

• One example hormone is oxytocin,and  vasopressin which is involved in pair bonding and parental behavior