Chapter 3: Methods of Cognitive Science Flashcards
Angiography
Book definition: “An imaging method used to evaluate the circulatory system in the brain. (p. 79)”
Block design experiment
Book definition: “An experiment in which the recorded neural activity is integrated over a “block” of time during which the participant is either presented a stimulus or performs a task. The recorded activity pattern is then compared to other blocks that have been recorded while doing the same task or stimulus, a different task or stimulus, or nothing at all. (p. 108)”
Blood oxygen-level-dependent (BOLD)
Book definition: “The BOLD signal is the change in magnetic resonance signal intensity of hydrogen ion concentration in the brain, which results from changes in local tissue oxygenation state. When neurons become more active, this triggers an increase in the amount of oxygenated blood entering local capillaries in the tissue. This alters the ratio of oxygenated to deoxygenated hemoglobin in the tissue. Because deoxygenated hemoglobin is paramagnetic, it disrupts the local magnetic properties of the tissue, and the MR signal intensity drops. Conversely, when oxygenated blood increases in response to local neuron activity, the MR signal intensity increases, and this is known as the BOLD response. The BOLD signal is an indirect measure of neural activity, and is delayed with respect to the neural activity that leads to the BOLD signal, taking about 2-3 seconds to begin, and about 5-6 seconds after the onset of neural activity to peak. (p. 107)”
Brain graph
Book definition: “A visual model of the connections within some part of the nervous system. (p. 110)”
Brain lesion
Book definition: “Structural damage to the white or gray matter of the brain. Lesions result from many causes, including tumor, stroke, and degenerative disorders such as Alzheimer’s disease. (p. 79)”
Cerebral vascular accidents
Book definition: “A rapid loss of brain function due to a compromise in the blood supply to the brain secondary to arterial occlusion or hemorrhage. (p. 74)”
The most common cause of stroke occurs when the normal passage of blood gets cut off by a foreign substance. Over years, atherosclerosis – the buildup of fatty tissue – occurs in the arteries. If part of this tissue breaks free, becoming an embolus, it can be carried by the bloodstream into the cranium through the large carotid or vertebral arteries. As the arteries become smaller, the embolus can become stuck, blocking the flow of blood. The lack of glucose and oxygen in the affected area will rapidly cause neuronal cell death.
Symptoms of stroke vary with the afflicted area. Small embolisms may get stuck in the cortex, leading to a sudden loss of speech, motor function, or vision. Larger embolisms may get stuck much earlier in the system, such as in the brainstem, leading to a loss of consciousness and death within minutes.
Other types of cerebral vascular disorders include ischemia, a lack of proper blood flow caused by low blood pressure or the partial blocking of an artery, and aneurysm, a weak spot in a blood vessel which may suddenly expand or burst.
Cognitive psychology
Book definition: “The branch of psychology that studies how the mind internally represents the external world and performs the mental computations required for all aspects of thinking. Cognitive psychologists study the vast set of mental operations associated with such things as perception, attention, memory, language, and problem solving. (p. 74)”
Computed tomography (CT / CAT)
Book definition: “A noninvasive neuroimaging method that provides images of internal structures such as the brain. CT is an advanced version of the conventional X-ray. Whereas conventional X-rays compress three-dimensional objects into two dimensions, CT allows for the reconstruction of three-dimensional space from the compressed two-dimensional images through computer algorithms. (p. 91)”
The typical spatial resolution for CT scanners is approximately 0.5 to 1 cm in all directions, with each point on the image reflecting an average density of that point and the surround 1 mm of tissue. This leaves it without the ability to discriminate between objects closer than 5 mm, leaving the approximately 4 mm thick cortex practically invisible.
As CT scans are based on density, the relatively high density of the skull and low density of fluid-filled ventricles make them easily visible, while the small difference in density between white and gray matter make those hard to distinguish.
Deep-brain stimulation (DBS)
Book definition: “The electrical stimulation of brain structures via an implanted electrode. Stimulation of the subthalamic nucleus, one of the nuclei of the basal ganglia, is used as a treatment for Parkinson’s disease. (p. 86)”
Although dramatic and sustained improvement is observed in many patients, the inner workings of the procedure are not fully understood.
A possible future alternative to DBS is the developing field of optogenetics, which uses genetic manipulation to make specific neurons sensitive to light. The neurons can then be stimulated by exposing the tissue to light.
Degenerative disorders
Book definition: “Disorders or diseases, either genetic or environmental, in which the function or structure of the affected tissues will continue to deteriorate over time. (p. 80)”
Degenerative disorders and their causes include:
- Alzheimer’s disease – tangles and plaques in the limbic and temporoparietal cortex.
- Parkinson’s disease – loss of dopaminergic neurons in the pars compacta of the substantia nigra within the basal ganglia.
- Huntington’s disease – atrophy of interneurons in caudate and putamen nuclei of the basal ganglia.
- Pick’s disease – frontotemporal atrophy.
- Progressive supranuclear palsy (PSP) – atrophy of brainstem, including colliculus.
Diffusion tensor imaging (DTI)
Book definition: “A neuroimaging technique employed using an MRI scanner that allows white matter pathways in the brain to be imaged. (p. 93)”
Double dissociation
Book definition: “A method used to develop functional models of mental and/or neural processes. Evidence of a double dissociation requires a minimum of two groups and two tasks. In neuropsychological research, a double dissociation is present when one group is impaired on one task and the other group is impaired on the other task. In imaging research, a double dissociation is present when one experimental manipulation produces changes in activation in one neural region and a different manipulation produces changes in activation in a different neural region. Double dissociations provide a strong argument that the observed differences in performance reflect functional differences between the groups, rather than unequal sensitivity of the two tasks. Compare single dissociation. (p. 84)”
Electrocortogram (ECoG)
Book definition: “A method to record electrical activity from the cerebral cortex by placing electrodes directly on the surface of the brain, either outside the dura or beneath it. (p. 102)”
Electroencephalogram (EEG)
Book definition: “A technique to measure the electrical activity of the brain. In EEG, surface recordings are made with electrodes placed on the scalp. The EEG signal includes endogenous changes in electrical activity (e.g., due to changes in arousal), as well as those triggered by specific events (e.g., stimuli or movements). (p. 99)”
Event-related design
Book definition: “A paradigm used in fMRI studies in which the BOLD response can be time-locked to particular stimuli or responses. Such designs require using delays or temporal variation in order to isolate the response to these events. (p. 108)”
Event-related potential (ERP)
Book definition: “A change in electrical activity that is time-locked to specific events such as the presentation of a stimulus or the onset of a response. When the events are repeated many times, averaging the EEG signals reveals the relatively small changes in neural activity triggered by these events. In this manner, the background fluctuations in the EEG signal are removed, revealing the event-related signal which great temporal resolution. (p. 100)”
The relatively small electrical responses to specific events can be observed only if the EEG traces are averaged over a series of trial. Averaging across tens or hundreds of trials removes the normally occurring “background” of the EEG signal, leaving the event-related potential visible.
After a stimulus, the earliest components are connected with sensory processing and occur within the first 100 milliseconds. After these, the following positive (P) and negative (N) waves are involved with different processes:
- The N100 and P100 waves are associated with selective attention.
- The N200 wave is known as the mismatch negativity component and is found when a stimulus is physically deviant from the preceding stimuli – e.g. when a G note is heard after a series of C notes.
- The P300 wave is seen when an attended stimulus is presented, especially if the stimulus is relatively rare.
- The N400 wave is observed when a stimulus is unexpected. It differs from the N200 wave in that the surprise event here might be a violation of semantics – e.g. “The cow jumped over the banana” – rather than a physical change.
Functional magnetic resonance imaging (fMRI)
Book definition: “A neuroimaging method that utilizes MRI to track blood flow changes in the brain that are thought to be correlated with local changes in neuronal activity. (p. 105)”
Magnetic resonance imaging (MRI)
Book definition: “A neuroimaging technique that exploits the magnetic properties of organic tissue. Certain atoms are especially sensitized to magnetic forces because of the number of protons and neutrons in their nuclei. The orientation of these atoms can be altered by the presence of a strong magnetic field. The atoms will then realign with the magnetic field and give off a radio frequency signal that can be measured by sensitive detectors. Structural MRI studies usually measure variations in the density of hydrogen ions in the tissue being scanned. Functional MRI measures changes over time in the signal intensity of the targeted atom. (p. 92)”
Optogenetics
Book definition: “A procedure in which a genetic manipulation is performed that will result in the expression of a photosensitive protein. The experimenter can then activate the neurons by exposing the tissue to light. The genetic manipulation can be modified such that the protein expression is limited to particular neural regions. (p. 72)”
In trials with rats, tiny optical fibers were implanted in the mouse brain, which could be used to transmit blue light to specific brain areas. When this method was used in a specific subregion of the amygdala, researchers were able to reduce anxiety in mice.
Optogenetics could have possible applications in humans, such as the above mentioned example, which might alleviate anxiety caused by PTSD.
Retinotopic map
Book definition: “Referring to a topographic map of visual space across a restricted region of the brain. Activation across the retina is determined by the reflectance of light from the environment. A retinotopic map in the brain is a representation in which some sort of orderly spatial relationship is maintained. Multiple retinotopic maps have been identified in the cortex and subcortex. (p. 97)”
Transcranial direct current stimulation (tDCS)
Book definition: “A noninvasive method in which a low voltage electrical current is created across the brain by applying two electrodes to the scalp. tDCS is hypothesized to potentiate neurons near the anodal electrode and hyperpolarize neurons near the cathodal electrode. (p. 89)”
Transcranial magnetic stimulation (TMS)
Book definition: “A noninvasive method used to stimulate neurons in the intact human brain. A strong electrical current is rapidly generated in a coil placed over the targeted region. This current generates a magnetic field that causes the neurons in the underlying region to discharge. TMS is used in clinical settings to evaluate motor function by direct stimulation of the motor cortex. Experimentally, the procedure is used to transiently disrupt neural processing, thus creating brief, reversible lesions. (p. 88)”
Epilepsy
Book definition: “None. (See pages 81-83)”
Epilepsy is a condition characterized by excessive and abnormally patterned activity in the brain, possibly resulting in seizures and temporary loss of consciousness.
Seizures range greatly in intensity: atonic seizures consist of brief but sudden loss of muscle tone, which can result in a fall, while grand mal seizures cause convulsions and a loss of consciousness lasting from minutes to hours.
Epileptic incidents can be clearly viewed on EEG recordings, where brain activity is marked by large-amplitude oscillations.
