PHYSIOLOGICAL PSYCH. EXAM 2 (CH 5-CH 8)

photopigment

a protein dye bonded to retinal, a substance derived from vitamin A; responsible for transduction of visual information.

transduction

(see sensory transduction) name of the process by which energy from the environment (ex. light) is converted to a change in membrane potential in a neuron. process that converts an external stimulus (ex. light, sound, heat) to an internal stimulus (the action potential generated by light-, sound-, or heat-detecting neurons).

rhodopsin

a particular opsin found in rods.

6.22 Describe the roles of region V5, MSTd, and the extrastriate body in the perception of movement.

Area V5 of the extrastriate cortex (area MT) contains neurons that respond to movement. Bilateral damage to the human brain that includes area V5 produces akinetopsia. MST neurons receive information from V5 and respond to complex patterns of movement, including radial, circular, and spiral motion. More specifically, MSTd neurons analyze optic flow. Movements of different body parts activate cells in the extrastriate body.

5.1 Explain what researchers can learn from studies that involve lesioning.

By lesioning a part of the nervous system, a researcher can observe the resulting changes in behavior to determine the function of that portion of the nervous system. The goal is to discover what functions are performed by different regions of the brain and then to understand how these functions are combined to accomplish particular behaviors. No one brain region or neural circuit is solely responsible for a behavior; each region performs a function (or set of functions) that contributes to performance of the behavior.

5.13 Describe how concordance rates in twins can be used to assess the genetic contribution to a behavior.

Concordance rates help researchers understand the contributions of genetic differences to variations in behavior. For example, if a disorder has a strong genetic basis, the percentage of monozygotic twins who are concordant for the diagnosis will by higher than that for dizygotic twins.

5.12 Review the steps involved in measuring brain chemicals using microdialysis.

First, a microdialysis probe is placed into the brain region of interest using stereotaxic surgery. A small amount of a solution similar to extracellular fluid is pumped into the brain through one of the small metal tubes into the dialysis tubing. The fluid circulates through the dialysis tubing and passes through the second metal tube, from which it is taken for analysis. As the fluid passes through the dialysis tubing, it collects molecules from the extracellular fluid from the brain, which are pushed across the membrane by the force of diffusion. A researcher can then analyze the brain chemical contents of the fluid that has passed through the dialysis tubing by an extremely sensitive analytical method.

5.9 Compare electrical and chemical neural stimulation, optogenetic methods, and transcranial magnetic stimulation.

Electrical and chemical stimulation of neurons are accomplished by passing an electrical current or injecting a chemical into a specific brain region through a cannula. Optogenetic methods are used to stimulate or inhibit particular types of neurons in specific brain regions. These neurons are genetically modified to express a protein that is wave-length sensitive. Researchers implant LEDs into the brain that can emit the corresponding wavelengths of light. Turning the light on and off allows the researcher to control the activity of the neurons that are light sensitive. Transcranial magnetic stimulation (TMS) uses a magnetic signal to stimulate or inhibit neurons beneath the TMS device. Unlike other methods of stimulating neural activity, TMS is noninvasive.

7.3 Compare the structure, function, and location of hair cells as they contribute to transduction of auditory information.

Inner and outer auditory hair cells are located on the basilar membrane. Hair cells contain rows of cilia and synapse with dendrites of bipolar neurons whose axons bring auditory information to the brain. Movement of the basilar membrane causes the cilia to move, bending back and forth. Cilia are arranged in bundles and bending the bundle of cilia causes receptor potentials. The inner hair cells are necessary for normal hearing. The outer hair cells are involved in altering the mechanical characteristics of the basilar membrane and influencing the effect of sound vibrations on the inner hair cells.

Compare recording neural activity using microelectrodes, macroelectrodes, and magnetoencephalography.

Microelectrodes can be used to record the electrical activity of individual neurons and must be placed into a single neuron. Macroelectrodes are used to record the summed electrical activity of many neurons in the vicinity of the electrode. Macroelectrodes can be placed in the brain or on the surface of the skull or scalp. Magnetoencephalography measures changes in magnetic fields of neurons and is used to detect groups of synchronously activated neurons.

6.19 Describe the contributions of retinal disparity, and the dorsal and ventral streams to visual perception of spatial location.

Most neurons in the striate cortex are binocular and contribute to depth perception via retinal disparity. The disparity-sensitive neurons found in the dorsal stream, which is involved in spacial perception, respond to large, extended visual surfaces, whereas those found in the ventral stream, which is involved in object perception, respond to the contours of three-dimensional objects.

6. 21 Explain how cells in the striate cortex identify orientation and function as movement detectors.

Most neurons in the striate cortex are sensitive to orientation and respond by increasing their rate of firing action potentials when a line is in a particular position in their receptive field.

6.17 Use examples from the research literature to support the roles of the ventral stream and fusiform face area in perception of form.

Recognition of visual patterns and identification of particular objects takes place in the inferior temporal cortex (part of the ventral stream) in primates. It is here that analyses of form and color are put together, and perceptions of three-dimensional objects and backgrounds are achieved. For example, studies have found neurons in the inferior temporal cortex that respond specifically to objects that have been seen many times but not to unfamiliar objects. Damage to the human extrastriate cortex can cause a category of deficits known as visual agnosia, a failure to recognize familiar objects or categories of objects, including faces. The fusiform face area is specifically devoted to facial recognition. Development of this region may be a result of extensive experience looking at faces; expertise with other complex stimuli such as artificial creatures (greebles) causes the development of circuits devoted to the perception of these stimuli as well. Development of the fusiform face area is altered in people with autism spectrum disorder, possibly because of insufficient motivation to become expert in recognizing other people's faces.

6.4 Contrast the location and function of rods and cones.

Rods are located throughout the retina, except in the fovea. They are sensitive to low intensity light but do not contribute to color or high acuity vision. Cones are prevalent in the central retina, including the fovea, and are responsible for color vision and acuity. There are more rods than cones in the human retina.

5.3 Describe the process of stereotaxic surgery.

Stereotaxic surgery involves using a stereotaxic atlas to identify a specific location in the brain. Once the location has been identified, the researcher places the head in a stereotaxic apparatus and positions a cannula over the correct location on the head. The researcher make san incision in the scalp of the anesthetized animal (or human), drills a hole in the skull, and lowers the cannula into place. The researcher makes the lesion (or in some cases implants an electrode or transplants tissue), removes the cannula, and the animal (or human) recovers from the anesthetic.

5.16 Summarize how targeted mutations can be used to reveal genetic contributions to a behavior.

Targeted mutations are used to change the production of a specific protein. The resulting change in behavior can be associated with the mutated protein.

6.3 Identify the structures of the eye and describe their function in visual processing.

The bones and muscles surrounding the eye aid in focusing an image on the retina. The pupil regulates the amount of light entering the eye. The lens is responsible for accommodation. The retina of the eye contains the photoreceptors (rods and cones), which detect light and transduce it into receptor potentials.

6.20 Discuss examples from the research literature that support the role of the extrastriate cortex in perception of spatial location.

The dorsal stream of the extrastriate cortex terminates in the parietal cortex. The parietal lobe is involved in spatial and somatosensory, and vestibular information to perform these tasks. Single-unit studies with monkeys and functional-imaging studies with humans indicate that neurons in the intraparietal sulcus (IPS) are involved in visual attention and control of saccadic eye movements (LIP and VIP), visual control of reaching and pointing (VIP and MIP), visual control of grasping and manipulating hand movements (AIP), and perception of depth from stereopsis (CIP).

6.11 Identify the role of the extrastriate cortex in visual processing, including the dorsal and ventral streams.

The extrastriate cortex is responsible for combining information from individual modules of the striate cortex to allow an individual to perceive objects and entire visual scenes. Each region of extrastriate cortex is specialized, containing neurons that respond to particular features of visual information, such as orientation, movement, spatial frequency, retinal disparity, or color. The ventral stream terminates in the inferior temporal cortex and is responsible for processing what an object is and what colors it has. The dorsal stream terminates in the posterior parietal cortex and is responsible for processing where the object is located and, if it is moving, its speed and direction of movement.

7.4 Describe the structure and function of the cochlear nerve, subcortical structures, and cortex in the auditory pathway.

The organ of Corti sends auditory information to the brain through the cochlear nerve. Auditory information travels from the cochlear nerve to the superior olivary nucleus, and on to the inferior colliculus, the medial geniculate nucleus, and finally to the auditory cortex. The auditory cortex has a tonotopic representation for auditory stimuli and is divided into primary and association areas. Processing in the auditory cortex progresses from the core region (primary cortex), to the belt region and then the parabelt region (association cortex). Cortical auditory processing consists of two streams. The anterior stream, which begins in the anterior parabelt region, is involved with analysis of complex sounds. The posterior stream, which begins in the posterior parabelt region, is involved with sound localization.

7.2 Identify the structures of the outer, middle, and inner ear.

The outer ear contains the pinna, ear canal, tympanic membrane. The middle ear contains the ossicles (malleus, incus, and stapes). The inner ear contains the cochlea, organ of Corti (including the basilar membrane, hair cells, tectorial membrane, and reticular membrane) and the round window.

6.6 Compare the characteristics of central and peripheral vision, including receptive fields and eye movements.

The receptive field of a neuron in the visual system is the part of the visual field that an individual "sees." At the periphery of the retina many individual receptors converge on a single ganglion cell, bringing information from a relatively large area of the retina and visual field. The fovea contains approximately equal numbers of ganglion cells and cones. These receptor-to-axon relationships explain the fact that our foveal (central) vision is very acute but our peripheral vision is must less precise. To keep stimuli from the environment projecting to the retina, particularly the fovea, the eyes make three types of movements: vergence movements, saccadic movements, and pursuit movements.

6.10 Identify the role of the striate cortex in visual processing, including functions of visual field mapping, CO blobs, and modular organization.

The striate cortex is the first cortical region involved in combining visual information from several sources. It receives visual input from the LGN and performs additional processing of this information, which it then transmits to the extrastriate cortex. The striate cortex contains 6 layers. Layer 4 contains 4 sublayers (4A, 4B, 4Cα, 4Cβ). CO blobs are groups of cells that receive information about color from the parvocellular and koniocellular layers of the LGN. Neurons in CO blobs of the striate cortex project to thin stripes, and neurons outside the blobs (in interblob areas) project to thick stripes and pale stripes of the extrastriate cortex. Neurons in the thin stripes receive information concerning color, and those in the thick stripes and pale stripes receive information about orientation, spacial frequency, movement, and retinal disparity. The striate cortex is divided into many modules, each containing thousands of neurons devoted to analysis of specific features of a portion of the visual field.

6.13 Differentiate between the trichromatic and opponent-color system theories.

The trichromatic theory explains that the eye detects different colors because it contains 3 types of receptors, each sensitive to a single hue (blue, green, or red). The opponent-color system theory explains that color represented in the visual system as opponent colors: red versus green and yellow versus blue. Research has revealed that cones are sensitive to blue, green, and red light, in support of the trichromatic theory and that retinal ganglion cells respond specifically to pairs of colors, with red opposing green and blue opposing yellow, in support of the opponent-color system theory.

6.8 Describe processing of information in the visual pathway, including the roles of the striate and extrastriate cortex.

The visual pathway begins in the photoreceptors of the retina, which synapse with bipolar and retinal ganglion cells. The axons of the retinal ganglion cells then send visual information to the rest of the brain by ascending through the optic nerves to the LGN in the thalamus. The neurons in the LGN send their axons through optic radiations to the striate cortex. From the striate cortex, visual information is sent to the extrastriate cortex.

ganglion cell

a neuron located in the retina that receives visual information from bipolar cells; its axons give rise to the optic nerve.

5.5 Differentiate between techniques for tracing efferent and afferent axons.

Tracing efferent axons allows researchers to learn about the target locations of sets of neurons. Using an anterograde labeling method, a chemical is injected into the region containing cell bodies, taken up with the cells, and transported to the terminals. Immunocytochemical methods use antibodies to identify the structures that receive input from the cell bodies. Tracing afferent axons allows researchers to learn about neurons that provide input to a region of interest. Using a retrograde labeling method, a chemical is injected into the target region and taken up by the terminal buttons. The chemical then travels to the cell body of the neuron. Immunocytochemical methods use antibodies to identify the structures that send input to the target region of interest.

retinal

a chemical synthesized from vitamin A; joins with opsin to form a photopigment.

opsin

a class of protein that, together with retinal, constitutes the photopigments.

parahippocampal face area (PPA)

a region of limbic cortex on the medial temporal lobe; involved in perception of particular ("scenes").

fusiform face area

a region of the visual association cortex located in the inferior temporal; involved in perception of faces and other complex objects that require expertise to recognize.

extrastriate body area (EBA)

a region of the visual association cortex located in the lateral occipitotemporal cortex; involved in perception of the human body and body parts other than faces.

sine-wave grating

a series of straight parallel bands varying continuously in brightness according to a sine-wave function, along a line perpendicular to their lengths.

sensory receptor

a specialized neuron that detects a particular category of physical events.

ventral stream

a system of interconnected regions of visual cortex involved in the perception of form, beginning with the striate cortex and ending with the inferior temporal cortex.

dorsal stream

a system of interconnected regions of visual cortex involved in the perception of spacial location, beginning with the striate cortex and ending with the posterior parietal cortex.

complementary colors

colors that make white or gray when mixed together.

visual agnosia

deficits in visual perception in the absence of blindness; caused by brain damage.

prosopagnosia

failure to recognize particular people by the sight of their faces.

parvocellular layer

one of the four outer layers of neurons in the dorsal LGN; transmits information necessary for perception of color and fine details to the primary visual cortex.

magnocellular layer

one of the inner two layers of neurons in the dorsal LGN; transmits information necessary for the perception of form, movement, depth, and small differences in brightness to the primary visual cortex.

brightness

one of the perceptual dimensions of color; intensity

saturation

one of the perceptual dimensions of color; purity

hue

one of the perceptual dimensions of color; the dominant wavelength.

cone

one of the receptor cells of the retina; maximally sensitive to one of three different wavelengths of light and hence encodes color vision.

rod

one of the receptor cells of the retina; sensitive to light of low intensity.

photoreceptor

one of the receptor cells of the retina; transduces photic energy into electrical potentials.

koniocellular layer

one of the sublayers of neurons in the dorsal LGN found ventral to each of the magnocellular and parvocellular layers; transmits information from short wave-length ("blue") cones to the primary visual cortex.

perception

the conscious experience and interpretation of information from the senses.

vergence movement

the cooperative movement of the eyes, which ensures that the image of an object falls on identical portions of both retinas.

retinal disparity

the fact that points on objects located at different distances from the observer will fall on slightly different locations on the two retinas; provides the basis for stereopsis.

posterior parietal cortex

the highest level of the dorsal stream of the visual association cortex; involved in perception of movement and spatial location.

inferior temporal cortex

the highest level of the ventral stream of the visual association cortex; involved in perception of objects, including people's bodies and faces.

negative afterimage

the image seen after a portion of the retina is exposed to an intense visual stimulus; consists of colors complementary to those of the physical stimulus.

pursuit movement

the movement that the eyes make to maintain an image of a moving object on the fovea.

retina

the neural tissue and photoreceptive cells located on the inner surface of the posterior portion of the eye.

sensory transduction

the process by which sensory stimuli are transduced into slow, graded receptor potentials.

sensation

the process in which specialized cells of the nervous system detect environmental stimuli and transduce their energy into receptor potentials.

saccadic movement

the rapid, jerky movement of the eyes used in scanning a visual scene.

fovea

the region of the retina that mediates the most acute vision of birds and higher mammals. color-sensitive cones constitute the only type of photoreceptor found in the fovea.

spatial frequency

the relative width of the bands in a sine-wave grating, measured in cycles per degree of visual angle.