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107 Cards in this Set

  • Front
  • Back
Empiricism
ALL that we know about the world around us is obtained through our senses
Goal of the study of the senses
to determine how we know what we know about the world (neural basis of sensory experience)
Psychophysics
-behavioral approach to understanding sensation and perception, based on empiricist/materialist philosophies
-examines the quantitative relationship between physical characteristics of a sensory stimulus and sensation/perception (psychological attributes of sensory experience)
Sensation
-what we feel when sensory receptors are stimulated
-related to the physical interaction of a stimulus with a sensory receptor
Law of Specific Nerve Energies
sensation depends on the TYPE of receptor activated, not the form of activation
Perception
-conscious awareness and interpretation of sensation
-related to which sensory pathway in the nervous system processes information from a receptor
-influenced by "top down" processes: cognition, attention, experience
-not directly related to the actual stimulus activating the receptor: it is the brain's interpretation of sensation, based on its internal model of reality
-hence, similar perceptions may arise from a variety of stimuli sharing a common feature, and may be fooled by illusions
Sensory Receptor
modified epithelial or nerve cell specialized to respond to the presence of a stimuli
Transduction
-the conversion of stimulus energy into electrophysiological response
-receptors are morphologically specialized to transduce specific forms of energy
Receptor Potential
-the change in membrane potential in a sensory receptor produced by transduction
-transduction current: the membrane current flow that results from sensory transduction
Sensory Transduction Cascade
-stimulation: stimulus interacts with primary sensory receptor
-accessory structure: shapes the interaction of the stimulus with the receptor (ex: lens of eye, pacinian corpuscle, outer/middle/inner ear structures)
Transduction Cascade
transduction
-the conversion of stimulus energy into electrophysiological response by a receptor
-receptors and their accessory structures are morphologically and physiologically specialized to respond optimally to specific forms of energy

Transmission-
-transduction current: membrane current in a receptor that results from transduction event
-receptor (generator) potential: change in membrane potential produced by transduction currents
-transmission: directly via generation of action potential, or indirectly via synaptic transmission to sensory afferents
Neuronal Tissue Type
-long receptors
-dendritic and axonal processes
-transmit information via action potentials
-examples: most mechanoreceptors and olfactory receptors
Epithelial Tissue Type
-short receptors
-NO axonal process
-synaptomimetic:
---functionally and morphologically similar to presynaptic nerve endings
---transduction currents release NT, but may not generate APs
-examples: visual, auditory/vestibular, taste receptors
"Classical Senses" - modality receptor classification
-smell (olfaction)
-taste (gustation)
-touch (somatosensation)
-pain (nociception)
-proprioception
---joint angle, muscle tension/length
---kinesthesia (movement, body in space)
---balance/orientation
-vision
-hearing (audition)
"Subliminal Senses" - modality receptor classification
-no conscious sensation

-blood pressure
-blood chemistry
-osmolarity
"Special Senses" - modality receptor classification
-electroreception (detection of weak electrical fields)
-magnetoreception (detection of weak electrical fields)
Mechanoreceptors
-touch/pressure
-pain
-hearing
-balance
-joint/muscle proprioception
Chemoreceptors
-taste
-smell
-pain
-itch
Electromagnetic Receptors
-vision
-electroreception
-magnetoreception
Thermoreceptors
-warm
-cold
Exteroceptive Site of Stimulation
Stimuli external to body, or on body surface
-hearing (audition)
-vision
-smell (olfaction)
-taste (gustation)
-touch (somatosensation)
Interoceptive Site of Stimulation
Internal Stimuli
-blood chemistry
-blood pressure
-osmolarity
Proprioceptive Site of Stimulation
Joints, muscles, tendons, vestibular apparatus
-balance
-position: joint angles
-movement (kinesthesia)
-force: resistance to movement
Nociceptive Site of Stimulation
Pain
-mechano-thermo-receptors
-chemoreceptors
Ways to classify receptors
-site of stimulation
-stimulus energy
-modality
-tissue type
Direct Transduction
-stimulus interacts directly with ion channels (similar to ionotropic synaptic receptors)
Indirect Transduction
-stimulus interacts with membrane receptors that regulate ion channels (similar to metabotropic synaptic receptors)
Information Coded by Sensory Systems
-modality: what form does the stimulus take
-intensity: how strong is the stimulus?
-timing: when did the stimulus occur?
-location: where is the stimulus in the world, and what is it's spatial relation to other stimuli?
Determinants of Modality
-type of energy in the stimulus
-type of sensory receptor specialized to respond to the stimulus ("labelled line")
Submodality
-each modality subdivides sensory "space" to resolve different attributes of a stimulus
-examples:
---audition: auditory receptors are tuned for sound frequency by location and mechanical properties of the sensory epithelium
---vision: rod and cone receptors in the eye are selective for particular wavelengths of light
---taste: taste receptors specialized for sweet, sour, salty, bitter
Intensity Coding
-intensity proportional to stimulus energy level (ie amplitude)
-response of the receptor (ie change in receptor potential) is proportional to stimulus amplitude
-receptor potential amplitude is encoded by firing rate of peripheral sensory neurons or primary sensory afferents (but code may change centrally)
-Adaptation: response may decline under constant stimulation (often interpreted as evidence that change is more important than steady-rate)
Temporal Coding
-temporal properties of a stimulus are encoded as changes in the pattern of sensory neuron activity in the periphery
---latency: time from stimulus onset to response
---onset/offset transients
---rate of stimulus change
-pattern codes for temporal features may be converted to a "rate/place" code centrally
Temporal Summation
-detection threshold is inversely proportional to the stimulus duration when stimulus duration is less than the temporal integration window
Receptive Field
the region of sensory space over which a receptor integrates energy
Organization of Receptive Fields
-receptive fields may be subdivided into regions that respond differentially to stimulation
-examples:
---visual RFs subdivided into a "center" and "surround" that elicit opposing responses to light
---auditory RFs may have excitatory and inhibitory response areas
Explicit Mapping of Space by Receptor Topography
-physical space directly (explicitly) "mapped" by spatial pattern (topography) of activated receptors

Vision:
-optics of the eye project visual stimuli onto a 2D sensory epithelium retina)
-objects in space fall on different regions of the retina

Somatosensation:
-location is encoded by position of sensory receptors on the body surface
Representation of Space from Neural Computation
Hearing
-sensory epithelium represents sound frequency, not space
-space perception derived from neural analysis of differences in spatial cues at the two ears generated by head

Smell:
-sensory epithelium sensitive to chemical odorants
-space computed centrally based upon reconstruction of odor "trails"

Taste:
-receptors for different "tastants" are segregated on the tongue
-but does taste have spatial dimensions?
Sensory Discrimination
what is the minimal perceptible difference (just-noticeable difference) between two stimuli/;
-Acuity
Acuity
a form of "two-point discrimination"
Ernst Weber
Weber "Laws"
-jnd is constant fraction of the absolute magnitude of the stimulus...
--when stimulus intensity is weak, jnd is small
--when stimulus intensity is strong, jnd is proportionately much greater

Weber Fraction:
-delta S/S = K
-Weber fraction is constant at all values of S
Fechner
Weber relationship is logarithmic
-jnd is proportional to the log of the stimulus intensity

S=k log R
Tone Frequency Discrimination
-jnd for frequency discrimination is constant at low frequencies but grows at higher frequencies
-Weber Fraction (deltaf/f) nearly constant from ~400 Hz - 2000 Hz
-above 2kHz, jnd grows steeply with frequency (ie deltaf/f not constant, Weber's Law is violated)
Visual Acuity
Acuity is related to:
-size of the receptive field (ie: diameter of the photoreceptor, relative to the projected image on the retina: smaller is better)
-spatial density (receptors/mm^2) of receptors in the retina: higher is better

Examples: a density of pixels on a tv screen or image sensor of a digital camera
The Chemical Senses
-oldest and most common of the senses
-present even in the simplest single-cell organisms
-transduction involves same principles and mechanisms used for communication among cells and tissues (chemical transmitters interacting with membrane receptors)
-Functions:
~finding food sources, judging value and safety of foods
~avoiding predators and hazardous environments
~social communication ("pheromones"), mating
~monitoring internal physiological state
Taste
-sensations relayed by taste receptor cells in the oral cavity
-foods active different, unique combinations of basic tastes
Flavor
-depends on both taste (gustation) and small (olfaction) - flavor is a multisensory perceptor
Somatosensory factors that influence taste:
-texture
-temperature
-pain
Tastants
-taste stimuli
-non-volatile, water-soluble (hydrophilic) molecules
-present in relatively high concentrations
Odorants
-odor stimuli
-volatile, aromatic (hydrophobic) compounds
-present in relatively low concentrations
Tastes
-sweet
-sour
-salty
-bitter
-umami (MSG, glutamate)
Nutrients (tastes)
salty, sweet
"attractive"
Anti-nutrients (tastes)
sour, bitter
"repulsive"
Taste Organs
-taste sensation arises from taste receptors located on the tongue and border between hard and soft palate
-NOT clearly localized to specific regions on the tongue or palate
Taste Buds
-morphologically specialized "accessory" epithelial structures containing taste receptor cells
-2000-5000 taste buds on human tongue
-50-100 receptors (taste cells) per taste bud, along with basal stem cells
-located in papillae:
~fungiform ("mushroom like") papillae: upper surface of tongue
~(circum-)vallate ("pimple-like": lined up in a "V" at back
~foliate ("folds", "ridges"): side
-taste buds within most paillae respond to only one of the basic tastes at low concentrations, but become less selective at high concentrations
Taste Cells
-modified epithelial cells ("short" sensory receptors)
-replaced ("turnover") about every 10 days
-differentiate from basal stem cells
Taste Receptors
-taste cells (like most receptors) are functionally and anatomically polarized
-apical membrane: microvilli
~protrude through taste pore into mucus of oral cavity
~provide large surface area to maximize contact with dissolved tastants
-basolateral membrane
~nucleus and other typical organelles
~synapses onto primary gustatory afferents (first-order taste neurons), which project into the central gustatory pathway
Taste Transduction
-mediated by both direct and indirect mechanisms
-some tastants directly carry currents through ion channels (direct transduction)
-other tastants bind selectively to specific G protein-coupled membrane receptors (indirect transduction)
-individual taste cells often use both types of transduction
Direct Transduction (taste)
-salty and sour
-salty: Na+ ions permeate amiloride-sensitive Na+ channels, directly depolarizing membrane
-Sour: protons (H+ ions) permeate amiloride-sensitive Na+ channels AND block K+ channels, directly depolarizing membrane
-depolarization opens Nav and Cav channels, leading to APs and transmitter release, respectively
Indirect Transduction (taste)
-bitter, sweet, and umami
-mediated by G protein-coupled pathways
~binding of tastant to receptor activates G protein/PLC/IP3 cascade
~IP3 elevates internal [Ca2+]
++IP3 causes release of Ca2+ from internal stores
++opens unique Ca2+ activated Na+ channel, depolarizing, membrane, opening Cav channels
~Ca2+ influx raises [Ca2+], activates transmitter release, stimulation of gustatory afferents
G protein-coupled Taste Receptors
Bitter receptors
- ~30 different bitter receptors derived from T2R gene family of receptors
-all T2R receptors give rise to a common "bitter" taste

Sweet and Umami Receptors
-T1R gene family
~two tightly-coupled receptor proteins, rather than one
~T1R2 + T1R3: sweet receptor
~T1R1 + T1R3: umami (amino acid) receptor
Early Processing of Tastes
-stimulation of taste produces: depolarizing receptor potential; RP sometimes generates APs, Ca2+ influx, transmitter release
-receptor potential magnitude proportional to both type AND concentration of tastant
-response selectively for basic tastes varies with receptor cell: 90% respond to two or more tastes
-gustatory afferents exhibit taste preferences: receive input from taste receptors with similar tastant selectively
Central Processing of Taste
taste cells --> primary gustatory afferents --> gustatory nucleus (brainstem) --> ventral posterior medial (VPM) nucleus of thalamus (forebrain) --> gustatory cortex
Brainstem Gustatory Pathway
-afferents from anterior 2/3 of tongue: facial nerve (cranial nerve VII)
-afferents from posterior tongue: glossopharyngeal nerve (CN IX)
-afferents from throat, palate, glottis/epoglottis: vagus nerve (CN X)
-taste axons from all three nerves project to the gustatory nucleus in medulla (a subdivision of the solitary nucleus)
Labeled-line coding
-Discrete Representation
-taste receptors VERY selective: respond only to one specific taste ("feature detectors")
-project to central targets through distinct afferent pathways, leading ultimately to specialized regions of cortex for each tastant
Population Coding
-distributed processing
-receptors partially selective: prefer one but respond to a variety of tastants
-no segregation of specialized taste regions in cortex
-unique taste perceptions arise from differential patterns of activity in the population
Are tastes mapped in brain by labelled lines?
Evidence for: taste cells express only one type of taste receptor (sweet receptor, bitter receptor)

Evidence Against: few taste cells, and even fewer taste afferents, respond to only one tastant

Why do taste cells expressing only one receptor contribute to more than one taste perception?
-taste receptors may have more than one transduction mechanisms (eg- direct and indirect)
-primary afferents innervate different types of taste cells located in same and different papillae ("convergence") and therefore are less selective than taste cells
The Sense of Smell
-olfaction plays a critical role in the survival of most animal species
-primary functions
~find and evaluating food
~avoiding noxious/toxic aerosols
~predatory-prey interactions
~social behavior and communication
++territoriality
++social aggregation
++mating (pheromones)
++maternal behavior
Odors and Odor Objects
-primary task of olfactory system is to identify odor objects of biological significance to the organism
-odor objects are complex and unique mixtures of two or more "odorants"
-odorants include:
~small, volatile molecules: alcohols, esters, aromatic compounds, fatty acids
~complex molecules: musks, steroids (often used as pheromones)
Organs of Smell
-sniffing actively brings odorants into nasal cavity to contact olfactory epithelium. Important and complex sensory-motor activity that has a significant impact on perception
-olfactory receptor neurons (ORNs) are found in olfactory epithelium of the nasal cavity
-olfactory epithelium secretes aqueous mucus within which odorants dissolve. Mucus contains proteins, antibodies, enzymes, salts, and odorant binding proteins that enhance concentration of odorants
Olfactory Epithelium
-composed of olfactory receptor neurons (ORNs), basal stem cells, and supporting cells, bilaterally located along nasal passage
-ORNs number in the tens of millions
-ORNs replaced every ~28 days by differentiation of basal stem cells (like taste cells, but one of the few places where new nerve cells are created in adulthood)
Olfactory Transduction
-apical pole of ORN forms a knob, from which tufted cilia extend into mucus layer
-odorants dissolved in mucus bind to odorant receptors (OR) location on ORN cilia
-binding stimulates unqiue G protein transduction cascade resulting in rise of cAMP levels
-cAMP directly opens cation channels, creating inward (depolarizing) Na+ and Ca2+ currents
-Ca2+ activated Cl- channels open, net outward Cl- flow substantially enhances inward depolarizing current
Transmission of ORN Activity
-transduction currents sum to generate APs in ORN
-termination activity:
~odorants diffuse away
~odorants broken down by enzymes
~cAMP activates other pathways ending transduction
-desensitization and adaptation: response to repetitive or prolonger stimulation wanes with time
Olfactory Receptor Proteins
-OR's are 7 transmembrane domain G protein coupled receptors, similar to B-adrenergic receptors
-mammals share over 1000 different OR genes (biggest gene family known)
-many are pseudogens, which do not normally express ORs
-only 350 genes in humans actually express ORs
-**each ORN typically expresses only one class of OR**
-therefore, only ~350 different types of human ORNs relay info for tens of thousands of different odors
Central Projections of Olfactory Nerve Fibers
-ORN axons become fibers in the olfactory nerve which projects to the olfactory bulb
-all ORNs expressing a particular OR converge onto one of two mirror locations, termed "glomeruli" in the OB
-each OB has ~2000 glomeruli
Odorant Selectivity
-each ORN expresses only one OR subtype
-olfactory epithelium contains four distinct spatial zones along A-P axis
-expression of given OR subtype is somewhat limited to a single epithelial zone
-each OR subtype is activated by many monomolecular odorants, and each odorant can activate many OR subtypes
-some OR subtypes are narrowly tuned responding differently to very similar odorants
-other OR subtypes broadly tuned, responding several odorant that differ in structure
-odorants may either activate or inhibit different ORs
Odorant Selectivity in ORNs
-most ORNs are odor "generalists" (they show a spectrum of responses to a variety of odors
-therefore, odor objects activate more than one type of ORN but to a different extent
-odorant concentration is also important but dynamic range of response in single ORNs is limited to about one order (factor of 10) of concentration magnitude
-conclusion: each ORN cannot uniquely code for either the identity or the strength of odorants
-central olfactory system must "disambiguate" identify and strength to discriminate odors (population coding)
Olfactory Glomerulus
-glomerulus is an anatomical and functional unit processing input from ORNs expressing the same OR
-glomerulus contains:
~ORN synaptic endings (many thousands)
~dendritic processes of 2nd order olfactory neurons (mitral, tufted, periglmerular)
-in each glomerulus, ~25,000 ORNs converge on dendrites of only ~100 second-order glomerulus cells
-population of glomeruli forms a topographic map of specific zones (and therefore OR genes) in the olfactory epithelium
Glomerular Circuity
-enhances odorant "contract"
-circuity is similar to retina:
~parallel input-output "vertical" pathways via mitral/tufted cells
~each mitral cells gets excitation from single glomerulus
~granule cell interneurons make "horizontal" inhibitory connections between mitral/tufted cells, mediating "lateral" inhibition
-lateral inhibition sharpens mitral cell selectively to improve odorant discrimination ("contrast enhancement")
Principles of Odor Map
-glomerulus is the basic structural and functional unit for odor mapping and processing in the olfactory bulb
~odorants activate specific spatial patterns of activity in glomerular lay of OB
~identified glomeruli can be correlated with odorant identity
-different odorants elicit activity in unique, overlapping populations of glomeruli; patterns may underlie discrimination
~homologous chemical series (alcohols, aldehydes) activate overlapping, but not identical, sets of glomeruli, reflecting similarity of chemical structure
-pattern of glomerular activation for an odor is similar across individuals
-increasing odor concentration "recruits" activity in additional glomeruli, which may give rise to different subjective perceptions
Olfactory Cortex
-piriform cortex
-orbitofrontal cortex: conscious perception of odors and tastes. Receives PC projections via MD nucleus of thalamus
-olfactory tubercle: projects to hypothalamus
-amygdala (emotion, social interactions, approach/avoidance)
-entorhinal cortex: connects to hippocampus, region of temporal lobe important for "working memory", particularly spatial memory
Processing Odors in Piriform Cortex
-PC is archicortex, has 3 layers (vs 6 in neocortex)
-topographic representation of odorants seen in olfactory bulb is lost in PC:
~odorants activate PC neurons over a wide area
~activation patterns for different odors are intermingles and overlap extensively with patterns activated by other odors
~the pattern of activation for an odorant is unique and similar across individuals
~PC neurons receive more input from other PC neurons than they do from OB projections
Representation of Odorants in Piriform Cortex
-single odorants activate unique pattern of elevated local activity over a wide area in PC
-pattern highly interdigitated with patterns from other odors
Cornea
primary refractive element in eye
Lens
secondary refractive element (for near-vision: "accommodation")
Iris
regulates amount of light entering the eye
Retina
epithelial tissue upon which image is projected, containing photoreceptors and associated neuronal circuity
Extraocular muscles
(horizontal, vertical and oblique pairs) control eye movements
-voluntary: saccadic and smooth pursuit
-reflexive: image stabilization re head movements
The Retina: a highly modified sensory epithelium
-macula: central region with highest density of photoreceptors
-fovea: in-folding of macula (primates only)
-optic disk: "blind spot", exit point for optic nerve (axons of retinal ganglion cells)
-pigmented epithelium: light absorbing basement membrane providing metabolic support
The Receptor Mosaic
-about 125 million photoreceptors in primate retina, packed into hexagonal array
-two classes of receptors: rods and cones
-ratio of photoreceptors to ganglion cells is near 1:1 centrally, increases with eccentricity in periphery
-central vision processed by fovea is highly over-represented in the output of the retina
Rods
-achromatic (best at medium wavelengths)
-low thresholds, function in low-light (scotopic) conditions
-extrafoveal- highest density in peripheral retina
Cones
-chromatic
-high thresholds, function in bright (photopic) conditions)
-three types of cones absorb different wavelengths:
~short (blue-violet): relatively rare
~medium (green): most common
~long (yellow-orange)
-clustered densely in the central retina (macula), particularly in the fovea of primates
Primate Fovea
-a pit or fold in the center of macula
-in humans, receives light from central 1 degree of visual space
-dominated by cones
-has the highest density of receptors, bipolar, and ganglion cells
-region of maximum visual acuity
Acuity is highest for central vision
-RFs in fovea are much smaller and more overlapping than peripheral retina
-ratio of photoreceptors to ganglion cells in fovea is much smaller (often 1:1) than in peripheral retina
-therefore, spatial resolution (two-point discrimination) is highest in foveal vision, declines with eccentricity
Photoreceptors
-modified epithelial cells (short receptors)
-out segment: transduction
~modified cilium, densely folded
~contains photopigments, transduce light into membrane current
~outer segments replaced daily
-inner segment: transmission
~transduction currents lead to transmitter release
Photoreceptor Transduction
-in the dark (unstimulated)
~cGMP-gated Na+ channels are open leading to inward (depolarizing) Na+ current (the so-called "dark current")
-exposed to light (stimulated)
~photos captured by photopigment rhodopsin
~rhodopsin "photo bleaching": Cis-retinal converts to trans-retinal, which dissociates from opsin
-opsin activates photoreceptor G-protein (transducin), which activates enzyme (PDE) that breaks down cGMP
-cGMP-gated Na+ channels close, inward current declines, membrane hyperpolarizes
Photoreceptor Sensitivity
-dark adapted humans can detect brief flash of only 5-7 photons falling on a small retinal area
-absorption of a single photon elicits a receptor potential change of ~1 mv, which peaks at 1 s, persists several seconds
-in dark-adapted rods:
~absorption of only ~30 photons reduces dark current /by half/
~absorption of 100 photons suppress dark current completely (maximal response)
-adaptation to light results in operational (dynamic) range for luminance of ~1000 cd/m^2
Photoreceptor Receptive Fields
-receptive fields in the visual system are defined in terms of degrees of visual space
-photoreceptor RF is spot-like, defined by the cross-sectional area of the outer segment
-response is modulated by luminance (more formally, illuminance, expressed in "lux" = lumens/m^2)
Retinal circuits create opponent receptive fields with contrast sensitivity
-vertical interactions: luminance response of photoreceptors is transmitted synaptically to bipolar cells, which then synapse on ganglion cells
-horizontal interactions: occur in synaptic "nests" at two levels
1) photoreceptor, bipolar, and horizontal cells
2) bipolar, ganglion, and amacrine cells
-result: bipolar and ganglion cells have "opponent", contrast-sensitive receptive fields
On- vs Off- Center Receptive Fields
-on-center cells are excited by spot of light confined to circular area in RF center
-off center cells are inhibited by the same stimulus
-on-center cells are inhibited by light falling on the "surround"
-off-center cells are excited by the same stimulus
-note: a population of receptors can generate both on- and off-center RFs, simply by reversing the "sign" of synaptic interactions
-"optimal stimulus" maximal contrast between center and surround
-"null" stimulus:
~diffuse light event illuminating center and surround elicits
~only slightly higher response than no stimulus at all (darkness)
-net result: retina mainly conveys information about local contrast, little about luminance
Color Vision
-P cells receive cone input, are color selective virtue of color opponent RFs:
~red-green (most numerous)
~blue-yellow
-red-green ganglion cells:
~receive antagonistic inputs from L and M cones
~L-on and M-off excited by red, inhibited by green in center of RF
~L-off and M-on are excited by green, inhibited by red
-M cells are achromatic, responding same to either L or M cones in center
Anatomic Substrate of Opponent RFs
-bipolar cells receive direct input from one or more receptors ("convergence"), forming the center of the RF
-bipolar cells receive indirect input from ring of receptors surrounding the center (via horizontal cells) forming the surround of the RF
Spatial Frequency Tuning
-response of RGCs to sinusoidal gratings depends on both contrast and spatial frequency (SF)
-contrast sensitivity is maximal at a single optimal or "best" SF
-best SF is related to the RF size
M Cells
-motion and spatial information processing
-in periphery
-large somata and RFs
-coarse spatial resolution (low)
-high contrast sensitivity
-respond better to motion
-optimized for large-scale moving patterns
-rapid conduction velocity
-rapid adaptation- sensitive to transients
P Cells
-fine features, shape and color processing
-in fovea
-small cell bodies and RFs
-fine spatial resolution (high)
-low contrast sensitivity
-respond well to stationary gradients
-optimized for fine features
-slow conduction velocity
-slow adaptation- sensitive to static images
Representation of Visual Space
-monocular fields and binocular fields
-optics of eye project upside-down and backwards image of moncular field onto each retina
~nasal views ipsilateral half of monocular field
~temporal views contralateral half of monocular field
Retinogeniculate Pathway
-optic nerves exit each eye and project bilaterally to the LGN of the thalamus
~fibers from temporal hemi-retina project to ipsilateral LGN
~fibers from the nasal hemi-retina cross midline ("decussate") in the optic chiasm, project to contralateral LGN
-LGN on each side projects ipsilaterally to the primary visual cortex
-result: info from each visual hemifield processed in contralateral hemisphere of visual cortex
Organization of Primate LGN
-primate LGN is organized into 6 distinct layers
-layers 1 and 2: magnocellular layers (large cell bodies, heavily stained); input from M-RGCs
-layers 3-6: parvocellular layers (small cells, lightly stained), input from P-RGHs