PSYCH 207: BRAIN PT 2

Growth Statistics of the Brain

The brain grows from 0 to 350 grams (about three-quarters of a period) during the prenatal period, but this growth doesn't stop at birth. The maximum brain weight of 1,350 grams (about three pounds) is achieved when the individual is about 20 years old. Most post-birth growth take place before the child's fourth birthday, but some changes continue through adulthood.

Phylogenetic division (evolutionary based)

hindbrain (most primitive), midbrain, forebrain

Hindbrain

The hindbrain develops originally as one of the three bulges in the embryos neural tube. The hindbrain consists of three major structures: the medulla oblongata, the pons, and the cerebellum.

The Brain Stem

A brain structure consisting of the medulla and pons of the hindbrain, as well as the midbrain and certain structures of the hindbrain. It composes about 4.4% of the total weight of an adult brain.

medulla oblongata

Found in the hindbrain, transmits information from the spinal cord to the brain and regulates life support functions such as respiration, blood pressure, coughing, sneezing, vomiting, and heart rate.

pons

Found in the hindbrain, acts as a neural relay centre, facilitating the "crossover" of information between the left side of the body and the right side of the brain, and vice versa. It is also involved in balance and in the processing of both visual and auditory information.

The Cerebellum

Found in the hindbrain, it contains neurons that coordinate muscular activity. It is one of the most primitive brain structures. It also governs balance and is involved in vernal motor behaviour and coordination. It has also been implicated in peoples ability to shift attention between visual and auditory stimuli, and in dealing with temporal stimuli such as rhythm. It controls coordinated movement; also involved in language and thinking.

10.5% of the weight of an adult brain.

Brain Lesions in the Cerebellum

Brain lesions in the cerebellum can cause irregular and jerky movements, tremors, and impairment in balance and of gait.

The Midbrain

In the middle of the brain. Many of the structures contained in the midbrain (such as the tectum and tegmentum) are involved in relaying information between other brain regions, such as the cerebellum and forebrain. Another midbrain structure, the reticular formation, helps keep us awake and alert and is involved in the sudden arousal we may need to respond to a threatening or attention-grabbing stimulus.

Forebrain

Some structures of the forebrain include, the thalamus, hypothalamus, hippocampus, amygdala, basal ganglia, cerebral cortex and more.

Thalamus

Located in the forebrain, the thalamus relays information acting as a neural relay center especially to the cerebral cortex. It is a switching station for sensory information and is involved in memory.

Hypothalamus

Located in the forebrain. The Hypothalamus controls the pituitary gland by releasing hormones, specialized chemicals that help to regulate other glands in the body. It also controls homeostatic behaviours, such as eating, drinking, temperature control, sleeping, sexual behaviours, and emotional reactions.

Hippocampus

In the forebrain and temporal lobe. Involved in the formation of longterm memories, memory and emotion. Specializes in the indexing of memories

Amygdala

In the forebrain and temporal lobe. It modulates strength of emotional memories, and is involved in emotional learning, aggression and basic emotional processing.

The Basal Ganglia

In the forebrain. Involved in the production of motor behaviour.

Spinal cord

transmits signals between the brain and the rest of the body

Cerebrum

The largest structure in the brain. It consists of a layer called the cerebral cortex, consisting of about a half-dozen layers of neurons with white matter beneath, which carries information between the cortex and the thalamus, or between different parts of the cortex.

cerebral cortex (cerebrum)

There is a division of four lobes: frontal (underneath the forehead), parietal (underneath the top rear part of the skull), occipital (at the back of the head), and temporal (on the side of the head).
The left and right hemispheres are connected by the corpus callosum (dense neural fibers), in the case of the frontal, parietal and occipital lobes and the anterior commissure, in the case of the temporal lobes. A structure known as the central sulcus divides the frontal and parietal lobes, the lateral sulcus, helps define the temporal lobe.
We have two lobes of each kind on each side-the right frontal, left frontal, right parietal, left parietal, and so forth.

Parietal Lobe

The parietal lobes contain the somatosensory cortex, which is contained in the postcentral gyrus, the area just behind the central sulcus. It is involved in the processing of sensory information from the body-for example, sensations of pain, pressure, touch, or temperature. In charge of spatial processing and involved languages.

Occipital Lobe

The occipital lobes process visual information, as well as the ability to process certain stimuli such as faces. Involved in simple motion processing.

Temporal lobe

The temporal lobes process auditory information, as well as the ability to process certain stimuli such as faces. Because the temporal lobes are right structures such as the amygdala and hippocampus, both involved in memory, damage to the temporal lobes can result in memory disruption as well.

frontal lobe

The frontal lobes have three separate regions. The motor cortex (located in the precentral gyrus), prefrontal cortex and the premotor cortex. It has been hypothesized that brain regions that show the most plasticity over the longest periods may be the most sensitive to environmental toxins or stressors.

The Motor Cortex

The motor cortex (located in the precentral gyrus) directs fine motor movement.

The Premotor Cortex

The premotor cortex is involved in planning fine motor movements, coordination and controlling basic movements.

The Prefrontal Cortex

The prefrontal cortex or lobe is involved in executive functioning-planning, making decisions, implementing strategies, inhibiting inappropriate behaviours, and using working memory to process information. Damage to certain parts of the prefrontal cortex can also result in marked changes in personality, mood, affect, and the ability to control inappropriate behaviour. The prefrontal cortex shows the longest period of maturation; to appears to be one of the last brain regions to mature. Interestingly, this region may also be one of the "first to go" in aging effects seen toward the end of life.

Localization of Function

The "mapping" of brain areas to different cognitive or motor functions; identifying which neural regions control or are active when different activities take place. Proposed by Franz Gall.

Faculty Psychology (Gall)

Faculty Psychology was the theory that different mental abilities, such as reading or computation, were independent and autonomous functions, carried out in different parts of the brain. Gall believed that different locations in the brain were associated with such faculties as parental love, combativeness, acquisitiveness, and secretiveness, to name a few.

Modularity in the brain, and developed phrenology (discredited).

phrenology (discredited)

Psychological strengths and weaknesses could be precisely correlated to the relative sizes of different brain areas.

The Problems with Phrenology

(1) That the size of a portion of the brain corresponded to its relative power.
(2) The different faculties were absolutely independent. We now know that different mental activities-for example, perception and attention-are not wholly distinct and independent, but rather interact in many different ways.
We also know that the overall size of a brain or brain area is not indicative of the functioning of that area. This is as there is a high level of dependence and we cannot isolate singular functions.

Aphasia

Paul Broca, in the early 1860s presented findings at a medical conference that brain injury to a particular part of the left frontal lobe (the posterior, inferior region) resulted in a particular kind of aphasia, or disruption of expressive language. This brain region has become known as Broca's area; injury to this area leads to a kind of aphasia known as a Broca's or nonfluent aphasia, in which the person is unable to produce many words or to speak very fluently.

Wernicke's Aphasia

Carl Wernicke announced the discovery of a second "language centre" in the brain, this one thought to control language and understanding (as apposed to language production). This region, which has become to be known as Wernicke's Area, is located in the superior posterior region of the temporal lobe, also typically in the left hemisphere. Patients with so-called Wernicke's Aphasia (also called fluent aphasia) are able to produce speech with seemingly fluent contours of pitch and rhythm. However, the speech often makes no sense and contains gibberish. Moreover, these patients show impairments in their ability to understand speech.

Lesions in Specific Brain Regions

Work by other neuropsychologists began to establish connections between lesions in particular brain regions and loss of specific motor control or sensory reception. Using research performed either on animals or as part of neurosurgical procedures intended to address problems such as epilepsy, scientists began to "map out" the portion of the frontal lobe known as the motor cortex.

Primary Somatosensory Cortex

In addition, neuropsychologists have mapped out a second area of the brain, located in the parietal lobe just behind the motor cortex, known as the primary somatosensory cortex. Like the motor cortex, the primary somatosensory cortex is organized such that each part of it receives information from a specific part of the body. As with the motor cortex, the total amount of "brain real estate" devoted to a particular part of the body is not proportional to the size of that body part. In other words, a large region of the body, such as leg, corresponds to only a small portion of the primary somatosensory cortex. A more sensitive part, such as fingers or lips, has a correspondingly larger amount of cortex devoted to it.

Brain Plasticity

Complicating this already involved picture of the brain organization is the notion of the plasticity of the brain. Some brain regions can adapt to "take over" functions of damaged regions, depending on the injury and the function involved. In general, the younger the patient and the less extensive the injury, the better is the chance of regaining function.

Lateralization of Function

Paul Broca's report of a language centre in his patients did more than argue for localization of function. Broca and many neuropsychologists since have been able to show that the two cerebral hemispheres seem to play different roles when it comes to some cognitive functions, especially language. We call this phenomenon lateralization.

Left Hemisphere Dominance in Language

Most individuals (around 95%) show a specialization for language in the left hemisphere. In these individuals, the left hemisphere is likely to be larger in size, especially in areas where language is localized. We say that these individuals has left-hemisphere dominance in language. A small percentage of people do not show such specialization, having language function in both hemispheres (these are called bilateralized individuals), and an even smaller percentage having language centres located in the right hemisphere.

The Right Hemisphere

Structurally, the right hemisphere often has larger parietal and temporal lobe areas, and it is speculated that it leads to better integration of visual and auditory information and better spatial processing by the right than the left hemisphere. The right hemisphere is associated with (analytics) working on geometric puzzles, navigation around familiar spaces, and even musical ability.

The Left versus the Right Hemisphere

Some describe the difference in function between the two hemispheres by labelling the left hemisphere as the analytical one and the right hemisphere as the synthetic one. The idea here is that the left hemisphere is particularly good at processing information serially, that is, information with events occurring one after another. Moreover, the two hemispheres are connected by a large neural structure known as the corpus callosum, which send information from one hemisphere to the other very quickly.

Computerized Axial Tomography Scan (CAT Scan)

X-ray computed tomography-also called X-ray CT, *Computerized Axial Tomography, or CT Scan-a technique in which a highly focused beam of X-rays is passed through the body from many different angles. Differing densities of body organs (including the brain) deflect the X-rays differently, allowing visualization of the organ. Typically, CAT scans of persons brain result in 9 to 12 "slices" of the brain, each one taken at a different level of depth. CAT scans depend on the fact that structures of different density show up differently. Bone, for example, is denser than blood, which is denser than brain tissue, which is in turn denser than cerebrospinal fluid. Recent brain hemorrhages are typically indicated by the presence of blood; older brain damage, by areas of cerebrospinal fluid. Thus clinicians and researchers can use CAT scans to pinpoint areas of brain damage and also to make inferences about the relative "age" of the injury.

Magnetic Resonance Imaging (MRI)

MRI provides information about neuroanatomy. MRI requires no exposure to radiation and often permits clearer pictures, as you can see in a picture of an MRI scan of a brain (high spatial resolution, but low temporal resolution). Someone undergoing an MRI typically likes inside a tunnel-like structure that surrounds the person with a strong magnetic field.
MRI scans are often the technique of choice, as they now produce textbook quality anatomy pictures of a brain. However, not everyone can undergo an MRI scan. The magnetic fields generated in an MRI scan interfere with electrical fields, so people with pacemakers are not candidates for MRI scan (pacemakers generate electrical signals). Nor are people with metal in their bodies, such as a surgical clip on an artery or a metal shaving in the eye. The magnetic field could dislodge the metal in the body, causing trauma. Metal anchored on hard surfaces, such as dental fillings, is not a problem. Because MRIs require people to lie very still in a tunnel-like machine that often leaves little room for arm movements, people with claustrophobia are also not good candidates for this technique.

Electrical Recording Methods

when neurons in the brain (or anywhere else, for that matter) fire, they generate electrical activity. Some animal research has involved placing electrodes in individual neurons to detect when and how often those single cells fire. Such work is not done with humans. Instead, the sum total of electrical activity generated by a large number of neurons comprises the information gathered.

Functional Magnetic Resonance Imaging (fMRI)

A newer technique that relies on the fact that blood has magnetic properties. Brain regions that are active how a change in the ratio of oxygenated to deoxygenated blood. Such fMRI scans use existing MRI equipment but provide clinicians and investigators with a noninvasive, nonradioactive means of assessing blood flow to various brain regions.
Low temporal resolution, high spatial resolution.

Electroencephalography (EEG)

Can be used to detect different states of consciousness. Mental electrodes are positioned all over the scalp. The waveforms record changes in predictable ways when the person being recorded is awake and alert, drowsy, asleep, or in a coma. EEGs provide the clinician or researcher with a continuous measure of brain activity.

Subtraction Technique

This logic has been adapted to develop functional maps of cognitive processes in the brain. He measured the time it took a person to respond (by making a keypress) to a light and subtracted this from the time needed to respond to a particular colour of light. His experiment revealed that discriminating colour requires about 50 msec of cognitive processing. In neuroimaging studies the same logic, termed subtraction technique, has been applied to isolate the brain region(s) contributing to a given cognitive process. That is, the relative amount of activation in a particular brain region needed for a given cognitive task can be measured by subtracting a control state (responding to a light) from a task state (discriminating colour).

Magnetoencephalography (MEG)

measures changes in magnetic fields generated by electrical activities of neurons. It has been called the magnetic equivalent of EEG. MEG gives a more precise localization of brain region activity then does EEG.

Single-Photon Emission Computed Tomography (SPECT)

Technique that measures cerebral blood flow. This basic technique is similar to a PET scan, but does not require some of the expensive equipment that PET scan requires; thus it is sometimes known as a "poor persons PET". Like CAT scans, however, PET and SPECT scans use radiation.

Event-Related Potential (ERP)

electrical recording technique that measures an area of the brains response to a specific event. Participants in an ERP study have electrodes attached to their scalp and are then presented with various external stimuli, such as sights or sounds. The recording measures brain activity from the times before the stimulus is presented until the time afterward. The brain waves recorded also have predictable parts, or components. That is, the shape of the waveform can vary depending on whether the participant expects the stimulus to occur or is attending to the location in which the stimulus appears, and whether the stimulus is physically different from other recent stimulus.

Positron Emission Tomography (PET)

This technique involves injecting a radioactively labelled compound (radioisotopes of carbon, nitrogen, oxygen, or fluorine subatomic particles that rapidly emit gamma radiation, which can be detected by devices outside the head). PET scans measure the blood flow to different regions of the brain, allowing an electronic reconstruction of a picture of a brain, showing which areas are most active at a particular time. A variation of the PET procedure involves measuring local metabolic changes instead of blood flow, using an injection of flurodeoxyglucose, a radioisotope structurally similar to glucose. Typically, PET scan visualizations are presented in colour. PET scans rely on the fact that when an area of the brain is more active more blood flows to it, and its cells take up more glucose from the blood vessels that penetrate it.