This lecture will focus on the gross neuroanatomy of the brain. Gross neuroanatomy refers to the large-scale structures of the nervous system that are visible without a microscope (i.e., macroscopic). It stands in contrast to microscopic neuroanatomy, which involves the cells and tissues of the nervous system that require magnification to be seen—such as neurons, synapses, and glial cells.
When we consider the brain’s relationship to mental processes, we typically think in terms of gross neuroanatomy. This is because mental processes are not determined by single neurons or even small clusters of neurons. Mental processes are not solo performances—they are orchestral performances. While there is a high degree of specialization among groups of neurons located in specific brain regions, these specialized populations must interact with others to carry out complex cognitive, emotional, and behavioral functions.
3 The Four Paired Lobes of the Brain
Figure 1. Diagram of the cerebral lobes, including the frontal, parietal, temporal, and occipital lobes. These lobes are associated with distinct functions such as planning, sensation, language, and vision. Source: Queensland Brain Institute.
The cerebral cortex (literally “bark”) of the brain is a large, thin sheet of gray matter approximately 2–4 mm thick (comparable to the thickness of 1–2 stacked nickels). A convenient way to organize your thinking about the anatomy of the cerebral cortex is to subdivide it into what are known as the lobes. Anatomically, there is no real division here. The cerebral cortex is continuous across these arbitrary boundaries. But the lobes are distinct in the types of mental functions they perform.
The are four sets of lobes, one set for each hemisphere:
Frontal lobes:
Primarily responsible for motor functions, planning, problem solving, speech production, and emotional regulation. Damage to the frontal lobes can lead to changes in personality and behavior, speech and motor impairments, and difficulties with decision-making.
Parietal lobes:
Involved in somatosensory processing and spatial attention. Damage to the parietal lobes can cause problems with sensory integration, spatial awareness, attention, and short-term memory maintenance.
Occipital lobes:
Primarily responsible for visual processing. Damage to the occipital lobes can result in visual difficulties, such as trouble identifying or locating objects.
Temporal lobes:
Involved in auditory perception, speech comprehension, and memory formation. Damage to the temporal lobes can result in difficulty understanding speech, impairments in long-term memory, and semantic issues, such as trouble categorizing objects.
4 Brain Gyri and Sulci
Figure 2. Diagram of the cerebral cortex (side view) highlighting key gyri and sulci. Gyri are the raised folds, and sulci are the grooves that increase the brain’s surface area and are important for organizing brain functions. Source: Wikimedia Commons.
Another way of organizing our understanding of the cerebral cortex is by examining its visible ridges and folds. A ridge in the sheet is known as a gyrus (plural: gyri), and a groove or fold is called a sulcus (plural: sulci). The folding pattern of the cortex into gyri and sulci is a hallmark of brain development, enabling an economy of space and functionality. This folding increases the total cortical surface area, which supports higher-order mental processes such as language and reasoning.
The gyri and sulci help us identify specific regions of the cerebral cortex beyond simply naming the general lobes. Prominent sulci include the central sulcus, which separates the frontal lobe from the parietal lobe, and the lateral scissure/fissure (also called the Sylvian fissure), which separates the temporal lobe from the frontal and parietal lobes. There are far too many gyri and sulci to memorize in a General Psychology course. Nonetheless, it’s useful to have some general familiarity with the terminology. For example, both the frontal and temporal lobes include superior (toward the top of the head), middle, and inferior (toward the bottom of the head) gyri.
5 Primary Somatosensory and Primary Motor Areas
Sensory input reaches the cerebral cortex through specialized primary sensory areas. The primary somatosensory cortex, located in the postcentral gyrus of the parietal lobe, is primarily responsible for processing touch, and also contributes to the perception of proprioception (body position), pain, and temperature. In contrast, other senses—vision, hearing, smell, taste, and balance—are processed by distinct primary sensory areas located in other regions of the brain.
Once processed in the primary somatosensory cortex, sensory information is sent to secondary sensory areas for further interpretation and integration.
Just across the central sulcus, in the precentral gyrus of the frontal lobe, lies the primary motor cortex, which is responsible for initiating voluntary muscle movements. Motor commands originate in regions such as the premotor cortex and supplementary motor area, and are relayed through the primary motor cortex to the muscles and other effectors of the body.
🧠 Fun fact: You might assume that the left half of the brain (called a hemisphere) controls sensation and movement on the left side of the body, and that the right hemisphere controls the right side. WRONG! In fact, the left hemisphere primarily controls the right side of the body, and the right hemisphere controls the left. This is because most sensory (afferent) and motor (efferent) nerve fibers decussate—that is, they cross over to the opposite side of the body as they travel through the brainstem or spinal cord. While there are some exceptions, this contralateral organization is a fundamental principle of brain function. Why this decussation occurs remains an open question in neuroscience. You can learn more by visiting this Wikipedia site.
The association areas of the cerebral cortex are responsible for the most complex functions. These areas receive refined sensory input from the secondary sensory areas. This is where higher-order intellectual processes are thought to occur.
Figure 3. Illustration of the sensory homunculus, which maps how different parts of the body are represented in the primary somatosensory cortex, located in the postcentral gyrus of the parietal lobe. The distorted size of each body region reflects the relative density of sensory receptors and the amount of cortical area devoted to processing its input. Regions like the hands, lips, and tongue appear oversized because of their heightened sensitivity. Source: Wikimedia Commons.
The primary motor cortex and primary somatosensory cortex are organized topographically; that is, specific parts of the body are mapped in an orderly, spatial layout across particular brain regions. This mapping is often illustrated by the cortical homunculus. The term homunculus, meaning little man, originally referred to a mythical figure thought to control the body from within. In neuroscience, it describes a diagram of the somatosensory (and motor) cortex that shows how different body parts are represented based on the amount of sensory (or motor) input they receive. The size of each region on the homunculus reflects the sensitivity of that body part—areas like the hands and lips appear larger because they require more detailed sensory processing.
🌐 Watch this!
Recall from a previous lecture that you learned about transcranial magnetic stimulation (TMS). TMS uses strong magnetic pulses to change the activity of neurons in the brain’s cortex. However, in order for TMS to work properly as a research or treatment tool, the strength of the pulses must be calibrated for the anatomy of each individual receiving the stimulation. To do this, pulses of specific strength and location are typically applied to the left primary motor area—specifically the hand-thumb area of the homunculus (test your knoweldge by thinking about which hand this ought to affect). Follow this link to a YouTube video that describes the process.
6 Hemisphere Dominance
In over 90% of right-handed individuals—and a majority of left-handed individuals—the left hemisphere is dominant for language-related activities such as speech production, reading, and writing. It also tends to support verbal, analytical, and mathematical processing.
The right hemisphere, by contrast, is more involved in non-verbal functions, including spatial awareness, facial recognition, musical perception, and processing emotional tone (prosody) in speech.
Unfortunately, this has led to a popular misconception—even among some in the scientific community—that certain cognitive functions are entirely performed in one hemisphere or the other. In reality, both hemispheres are typically involved in complex mental functions. This is why we use the term dominance: it acknowledges that while one hemisphere may play a larger role in a given function, its involvement is rarely exclusive or absolute.
A related popular idea is that people are either “right-brained” or “left-brained”—with left-brained individuals seen as more analytical and logical, and right-brained individuals as more creative and intuitive. While this notion has some loose roots in real differences in hemisphere function, it oversimplifies how the brain actually works. As the discussion above shows, most mental processes involve both hemispheres working together, making the left-brain/right-brain distinction more metaphor than scientific fact.
Figure 4. Diagram illustrating brain lateralization. The left hemisphere is generally associated with analytical thinking, logic, language, and detail-oriented tasks, while the right hemisphere is more involved in holistic processing, creativity, emotional expression, and spatial ability. While these tendencies are supported by research, the image is a simplification. In reality, most complex mental functions involve both hemispheres working together in an integrated way. Source: Adapted educational resource.
7 Localization of Mental Function
A question that has engaged the neuroscience community for centuries is the functional organization of the brain with respect to mental functions. As noted above, the four paired lobes of the brain do have general functional differences. But beyond the lobes, do very specific parts of the brain control very specific mental functions? For example:
What parts of the brain produce versus comprehend speech?
Are memories stored in specific parts of the brain?
Is there a “fear center” of the brain?
What we are describing here is the so-called localizationist vs. connectionist debate in psychology and neuroscience—that is, whether cognitive abilities are tied to discrete, isolated regions or distributed across interconnected networks. It would take an entire course in cognitive neuroscience to fully explore the mental functions that are understood in terms of specific versus distributed brain regions. But a simple answer to this question is that the localizationists and connectionists were both right to some degree. For most cognitive functions, specific brain regions are critical, but these regions function as part of interconnected networks, and the full network is needed for mature brain and mental functioning.
Figure 5. Simplified illustration of a brain network. Each circle (or node) represents a brain region, and the lines between them indicate functional or structural connections. This diagram reflects the modern connectionist view in neuroscience, where mental functions are thought to emerge from the interaction of distributed regions rather than isolated centers. Source: Wikimedia Commons.
For example, in the case of speech comprehension and production, two specific brain areas—named after the physicians who first described their relevance in patients with aphasia (speech difficulties)—are clearly tied to these functions. Broca’s area, a region in the frontal lobe, is critical for speech production. In contrast, Wernicke’s area, located in the temporal lobe, is essential for speech comprehension. People with damage to Broca’s area often struggle to produce fluent speech (e.g., “I… uh… not… want…”), while those with damage to Wernicke’s area often have difficulty understanding others and may produce fluent but nonsensical speech. However, Broca’s area and Wernicke’s area are themselves interconnected by white matter pathways and are also connected to other critical regions as part of a broader language network—likely even multiple, overlapping networks.
🎥 Watch this before continuing!
A Memory Is a Functional Network of Neurons.
🧠 Clinical insight: In Alzheimer’s disease, neurons in the hippocampus and surrounding parahippocampal areas (regions of the temporal lobe that are closely connected to the hippocampus) die due to the accumulation of neurofibrillary tangles and amyloid plaques. Alzheimer’s is a progressive neurodegenerative disease, meaning it worsens over time. As the disease advances, affected individuals gradually lose the ability to form new memories and experience other cognitive difficulties, eventually leading to dementia—a clinical term for significant impairments in cogntive functioning that interferes with activities of daily living. While there is currently no cure for Alzheimer’s, research suggests that maintaining a healthy lifestyle—including a balanced diet, regular physical activity, limiting alcohol use, and getting adequate sleep—may help reduce your risk of developing the disease.
The amygdala, another limbic system structure, is well known for its role in fear processing. Patients with sufficient damage to the amygdala lose the ability to feel fear—even adaptive fear that helps people avoid danger. However, the amygdala does not only process fear. It appears to be involved in a range of emotional experiences, often in conjunction with other brain structures such as the insula (a portion of cortex in the temporal lobe that is folded inward and “insulated”) and the anterior cingulate cortex (the frontmost part of the cingulate cortex, which runs along the midline of the brain between the two hemispheres).
The topic is complex, but the takeaway is simple: we should avoid the temptation to reduce complex mental functions to the activity of a single neuron or localized brain region. While the adult human brain does show remarkable specialization, it is ultimately composed of multiple structurally and functionally connected networks that work together to support higher-order mental functions.
🎥 Watch this!
With these caveats in mind, watch this basic YouTube video on the functional organization of the brain at the following. Remember that introductory explanations of brain organization—especially for higher mental functions—are often oversimplified. Still, this video provides a helpful overview.
🌐 Explore this!
Use this link to the brainfacts.org 3D brain. When you first arrive at the website, you’ll receive a short tutorial on how to interact with the 3D model. Click on the dropdown menu in the upper left corner and select the following structures:
Left hemisphere
Right hemisphere
Frontal lobe
Occipital lobe
Parietal lobe
Temporal lobe
Now spend some time exploring other structures in the 3D brain that you learned about in this lecture guide.
