Brain Structure and Function: Lobes and Hemispheres
Brain Structure and Function
Cerebral Cortex
The cerebral cortex is the outer layer of the cerebral hemispheres, containing 70% of neurons in the CNS. It is composed of five layers of neurons and a plexiform layer (composed of fibers). The convolutions of the cortex allow the large cortical surface to fit a small space.
- Grooves: Channels or grooves
- Fissures: Deeper grooves
- Convolutions: Deformations produced by the folds
Cerebral Hemispheres
Left Hemisphere
The left hemisphere controls logical functions and is involved in the center of expressive power. It specializes in articulate speech, motor control of the phono-articulatory apparatus, handling information, logical processing of information in series, handling mathematical information, verbal memory, logical aspects of language (grammar, organization, syntax), aural discrimination, focused attention, time management, planning, implementation, decision-making, and long-term memory. Intelligence tests primarily measure the activity of this hemisphere.
Right Hemisphere
The right hemisphere is inclusive and central to visual-spatial abilities. It is specialized in nonverbal sensations, feelings, and special skills (visual, audio, non-linguistic artistic and musical). It conceives situations and thinking strategies in a total way, conveying and transmitting information as a whole. The method of preparation used by the right hemisphere is consistent with the type of immediate response required in visual processes and spatial orientation. Patients with tumors in the right hemisphere may not recognize objects, places, or people.
Corpus Callosum
The corpus callosum is the largest bundle of nerve fibers (central angle) in the human brain. It serves as a communication channel between the two hemispheres, allowing both sides of the brain to work together and complement each other. Agenesis results in a split-brain condition.
Cortex Intellectual Skills
Intellectual skills include analysis, synthesis, abstraction, mathematical skills, verbal skills, induction, and deduction.
Lobes
Frontal Lobe
The frontal lobe is the most anterior part of the brain, responsible for voluntary movements and planning. It is important for personality and intelligence. Injury here can cause hemiplegia. The motor cortex is located in the back of the frontal lobe, along the path that separates it from the parietal lobe. It occupies 1/3 of the complete cerebral cortical surface and is the seat of abstract thought. The accident of Phineas Gage resulted in emotional, motor, and cognitive changes, including a lack of planning and caution, mechanical or robotic behaviors, altered social conduct, apathy, and bouts of euphoria.
It is responsible for: directing behavior towards a goal, including attention, planning, sequencing, and refocusing on the action. Damage to this region produces a deficit in social skills and behavior.
Broca’s area: Specializes in word formation (area of dominant left hemisphere).
Broca’s Aphasia: Loss of ability to produce speech.
Parietal Lobe
The parietal lobe is primarily responsible for receiving sensations of touch, heat, cold, pressure, balance, and coordination. It includes the somatosensory cortex, just below the groove that separates this lobe from the frontal lobe.
Injuries to this area cause: Impaired image recognition, visuospatial deficits, astereognosis (inability to perceive by touch), and prosopagnosia (inability to recognize faces or others).
Temporal Lobe
The temporal lobe contains Wernicke’s area, right next to the auditory cortex. It is important in complex visual tasks such as face recognition and is the primary olfactory center of the brain. It also receives and processes information from the ear, helps to maintain balance and equilibrium, and regulates emotions and motivations such as anxiety, pleasure, and anger. Additionally, it houses the primary auditory cortex and auditory association cortex, which contain several representations of sound frequencies, known as tonotopic maps, important for the perception of auditory properties such as pitch, location of rhythm, and timbre. Each ear projects stimuli to both hemispheres.
Auditory Cortex: Specializes in hearing and is located near the temporal lobe, with connections to the parietal and frontal lobes.
Occipital Lobe
Located in the back of the head, the occipital lobe‘s visual cortex receives information from the eyes and specializes in vision.
Vital functions include: visual acuity, pattern vision, and discrimination of form and figure-ground.
Damage to this area produces cortical blindness or total blindness.
The lobes are called unskilled, and the association cortex, in addition to connecting sensory and motor cortices, is where our thought processes occur and many of our memories are ultimately stored.