Parietal & Occipital lobes, Basal Ganglia, Thalamus, Internal Capsule

Basic Neuroanatomy

Planes of Anatomy

Understanding anatomical planes is essential for describing brain structures, interpreting imaging, and communicating clinical findings accurately.

Sagittal Plane
The sagittal plane divides the body into left and right portions. When the plane runs exactly down the midline, it is called the midsagittal plane. Structures closer to the midline are described as medial, while structures farther from the midline are described as lateral. This plane is particularly useful for visualising midline brain structures such as the corpus callosum and brainstem.

Axial (Horizontal) Plane
The axial plane divides the body into upper (superior) and lower (inferior) portions. This is the most commonly used plane in CT and MRI imaging. Structures are described as superior or inferior relative to one another. Axial views are particularly useful for following white-matter tracts and identifying deep grey matter structures.

Coronal (Frontal) Plane
The coronal plane divides the body into anterior (front) and posterior (back) sections. Structures can be described as anterior or posterior. This plane is especially helpful for understanding relationships between the frontal lobes, basal ganglia, and thalamus.

Understanding Brain Scans

In clinical imaging, brain scans are conventionally viewed from the feet upward, meaning the patient’s right side appears on the left side of the image. This orientation is often counterintuitive and must be consciously remembered when interpreting scans.

Recognising which anatomical plane is being used is essential. Axial images can be mentally reconstructed into sagittal and coronal views, allowing clinicians to build a three-dimensional understanding of lesion location, structural displacement, and functional risk.

Skull Anatomy and Entry Points

Before modern imaging techniques such as CT and MRI were available, neurosurgeons relied on external skull landmarks to estimate the position of internal brain structures. While imaging has largely replaced this practice, anatomical surface landmarks remain important, particularly during surgical planning.

For example, the region beneath the jaw and temporalis muscle provides a surface landmark for the Sylvian fissure, which overlies the temporal lobe. Understanding these relationships is crucial for safe surgical access and avoiding damage to critical cortical regions.

Structure of the Brain

Grey Matter and White Matter

Grey Matter
Grey matter consists primarily of neuronal cell bodies, dendrites, and synapses. It appears grey because it lacks myelin. Grey matter forms the cerebral cortex and deep grey matter structures such as the basal ganglia and thalamus. These regions are responsible for processing, integration, and decision-making.

White Matter
White matter is composed mainly of myelinated axons. Myelin gives white matter its lighter appearance and allows rapid signal transmission between distant brain regions. White matter enables communication between cortical areas, subcortical nuclei, and the spinal cord.

Brain Lobes

Overview of the Lobes

The brain is divided into five lobes: the frontal, parietal, temporal, occipital, and insula. Each lobe has characteristic anatomical boundaries and specialised functions, but effective brain function depends on communication between them.

Frontal Lobe

The frontal lobe is the largest cerebral lobe and is involved in motor control, planning, language production, and executive functions.

  • Medial border: includes the cingulate gyrus, which is involved in emotion and motivation.

  • Lateral border: defined by the Sylvian fissure, separating it from the temporal lobe.

  • Superior border: limited by the skull.

  • Inferior border: forms the base of the frontal lobe above the orbits.

The primary motor cortex lies in the precentral gyrus. During neurosurgery, electrical stimulation is used to map this region and avoid damage to essential motor areas and adjacent language regions such as Broca’s area.

Temporal Lobe

The temporal lobe contains key structures involved in memory, emotion, and auditory processing.

The amygdala plays a central role in emotional processing, while the hippocampus is essential for memory formation. The lateral surface contains the superior, middle, and inferior temporal gyri, separated by sulci.

The primary auditory cortex is located in Heschl’s gyrus, which is uniquely oriented perpendicular to the other temporal gyri. This orientation is a useful anatomical landmark on imaging and specimens.

Parietal Lobe

The parietal lobe is primarily responsible for sensory processing and integration.

The postcentral gyrus contains the primary somatosensory cortex and lies immediately posterior to the central sulcus. The parietal lobe integrates tactile, proprioceptive, and spatial information.

Damage to the dominant parietal lobe can result in Gerstmann syndrome, which includes left–right disorientation, finger agnosia, dysgraphia, and dyscalculia. Lesions of the non-dominant parietal lobe often cause hemispatial neglect.

Occipital Lobe

The occipital lobe is dedicated to visual processing.

It is defined by the parieto-occipital sulcus and contains the primary visual cortex along the calcarine sulcus. Each occipital lobe processes visual information from the opposite visual field.

Damage to this region leads to visual field defects such as homonymous hemianopia rather than complete blindness.

Insula

The insula lies deep within the lateral sulcus and is covered by the frontal, parietal, and temporal opercula.

It is involved in sensory integration, particularly pain perception, visceral sensation, and taste. The insula has distinct short and long gyri, which can be identified on imaging and surgical exposure.

Neuroanatomical Relationships in Clinical Context

Understanding neuroanatomy is essential for surgical planning and neurological localisation.

Electrode placement is used in epilepsy surgery to identify seizure-generating regions.
Functional mapping using intraoperative stimulation allows surgeons to test motor and language function in real time, helping preserve critical areas while removing pathological tissue.

Deep Grey Matter and Basal Ganglia Circuits

Definitions and Importance

The basal ganglia include the caudate nucleus, putamen, and globus pallidus, along with associated structures such as the subthalamic nucleus and substantia nigra.

These nuclei regulate movement by modulating cortical motor output rather than initiating movement directly. They operate through direct (facilitatory) and indirect (inhibitory) pathways, maintaining balanced motor control.

Clinical Relevance

In Parkinson’s disease, degeneration of dopaminergic neurons in the substantia nigra leads to excessive inhibitory output from the basal ganglia. This results in bradykinesia, rigidity, and tremor.

Therapies such as deep brain stimulation aim to restore balance within these circuits by modulating abnormal neural activity.

Thalamus

Function and Structure

The thalamus acts as a central relay station, transmitting sensory and motor information to the appropriate cortical areas.

It is divided into multiple nuclei, including:

  • the lateral geniculate body for visual information,

  • the medial geniculate body for auditory information,

  • ventral nuclei for sensory and motor integration.

Clinical Application

The thalamus plays an important role in epilepsy, pain syndromes, and disorders of consciousness. Understanding thalamic involvement allows clinicians to tailor treatments, including surgical and neuromodulatory approaches, to reduce seizure activity and improve outcomes.

Conclusion

A strong foundation in neuroanatomy underpins safe and effective clinical practice. Understanding anatomical planes, cortical organisation, deep grey matter circuits, and their clinical relevance is essential, particularly in surgical fields such as neurosurgery and epilepsy management. Integrating anatomical knowledge with imaging, functional mapping, and clinical reasoning allows precise localisation and optimal patient care.

BORDERS OF THE CEREBRAL LOBES

Detailed Identification Notes

Core principle (read this first)

Cerebral lobes are not separated by walls. They are divided by consistent sulci and fissures that act as landmarks.
If you can reliably find:

  • the central sulcus

  • the lateral (Sylvian) fissure

  • the parieto-occipital sulcus

  • the calcarine sulcus

you can identify every lobe and most major gyri.

Frontal lobe

Borders

Posterior border

  • Defined by the central sulcus

  • Everything anterior to the central sulcus is frontal lobe

Inferior border

  • Defined by the lateral (Sylvian) fissure

  • Separates frontal lobe from temporal lobe

Medial border

  • Defined by the cingulate sulcus

  • Structures above it belong to the frontal lobe

Anterior border

  • The frontal pole (no sulcus, just the most anterior cortex)

Key gyri you must identify

Precentral gyrus

  • Lies immediately anterior to the central sulcus

  • Contains the primary motor cortex

  • If you see a gyrus hugging the central sulcus on the anterior side → it’s precentral

Superior, middle, and inferior frontal gyri

  • Run anterior–posterior

  • Separated by superior and inferior frontal sulci

Inferior frontal gyrus

  • Subdivided into:

    • pars opercularis

    • pars triangularis

    • pars orbitalis

  • This is where Broca’s area lies (dominant hemisphere)

Parietal lobe

Borders

Anterior border

  • The central sulcus

  • Everything posterior to it is parietal lobe

Posterior border

  • Defined by the parieto-occipital sulcus

  • On the lateral surface, this is approximated by a line to the pre-occipital notch

Inferior border

  • Defined by the lateral fissure

  • Separates parietal from temporal lobe

Medial border

  • Paracentral lobule and medial surface posterior to central sulcus

Key gyri and subdivisions

Postcentral gyrus

  • Lies immediately posterior to the central sulcus

  • Primary somatosensory cortex

  • This is the most important parietal landmark

Superior parietal lobule

  • Lies posterior to postcentral gyrus

  • Above the intraparietal sulcus

  • Involved in spatial integration

Inferior parietal lobule

  • Lies below the intraparietal sulcus

  • Subdivided into:

    • Supramarginal gyrus (curves around end of Sylvian fissure)

    • Angular gyrus (curves around end of superior temporal sulcus)

These two gyri are extremely exam-relevant.

Temporal lobe

Borders

Superior border

  • Defined by the lateral (Sylvian) fissure

  • Everything below it is temporal lobe

Posterior border

  • An imaginary line from the parieto-occipital sulcus to the pre-occipital notch

Anterior border

  • The temporal pole

Medial border

  • Parahippocampal gyrus and uncus on medial surface

Key gyri you must identify

Superior temporal gyrus

  • Lies immediately below the lateral fissure

  • Contains auditory cortex and Wernicke’s area posteriorly

Middle temporal gyrus

  • Lies below the superior temporal sulcus

Inferior temporal gyrus

  • Lies below the inferior temporal sulcus

Heschl’s gyrus

  • Located on the superior surface of the temporal lobe

  • Runs perpendicular to the long axis of the temporal gyri

  • This orientation is a classic exam clue

Occipital lobe

Borders

Anterior border

  • Defined by the parieto-occipital sulcus on the medial surface

  • Approximated laterally by the pre-occipital notch

Posterior border

  • The occipital pole

Inferior border

  • Continuous with the temporal lobe inferiorly

Key landmarks

Calcarine sulcus

  • Runs horizontally on the medial surface

  • Primary visual cortex lies on either side of it

Cuneus

  • Lies above the calcarine sulcus

Lingual gyrus

  • Lies below the calcarine sulcus

If you see the calcarine sulcus → you are in the occipital lobe.

Insula

Borders and identification

The insula is not visible on the surface.

It lies:

  • deep to the lateral fissure

  • covered by the frontal, parietal, and temporal opercula

To identify the insula:

  • mentally “open” the Sylvian fissure

  • look for a triangular cortical area with short anterior gyri and long posterior gyri.