Chapter 7 Life-Span Development of the Brain and Behavior PDF

Chapter 7 Life-Span Development of the Brain and Behavior Embryonic Development - Zygote – fertilized egg; single cell that undergoes rapid division - Blastocyst – hollow sphere of pluripotential cells that eventually form the embryo - Gastrula – 3 layer form of partially diffe...

Chapter 7 Life-Span Development of the Brain and Behavior Embryonic Development - Zygote – fertilized egg; single cell that undergoes rapid division - Blastocyst – hollow sphere of pluripotential cells that eventually form the embryo - Gastrula – 3 layer form of partially differentiated blastocyst (ectoderm, mesoderm, endoderm), prepare for organ development - Embryo – developing organism during early stages of pregnancy, characterized by formation of 3 germ layers - Fetus – later stage of development where organism becomes recognizable in relation to mature form Nervous System development - Complex process that begins at conception and continues through early childhood - Key stages: (important to form brain/spinal cord) - Neurogenesis: process of generating new neurons from progenitor cells/ neural stem cells; produce new cells - Embryonic development and certain brain regions throughout life - Occur in ventricular zone - Progenitor cells undergo symmetrical division (radial glia), later transition to asymmetrical division – produce glioblasts and neuroblasts - Rate and timing of neurogenesis cary across different regions of neural tube - 7wks: production of neuroblasts and glioblasts begins → form specialized neuronal and glial cell types - Migration: Newly formed neurons migrate to designated locations in brain; guided by radial glia that provide scaffold (temporary network of projections from VZ to pial surface) - Radial glia extend to temporary network of projections to ventricular zone to pial surface to guide outward migration - 1. Preplate zone (PP) established by wave of migration from ventricular zone (VZ) - 2. Second wave migrates through intermediate zone (IZ) to split preplate into marginal zone (MZ) and subplate (SP) - 3. Successive waves migrate out to expand cortical plate (CP) in inside-out manner (layers 1-6-5-4-3-2)  - Tangential migration contributes to formation of subcortical neurons and interneurons – crucial for cortical organization - Focal cortical dysplasia can result in migration process → devp disorders - Differentiation: once target location reached, neurons differentiation into specific types of neurons and glial cells - Acquire unique functions - Dividing pluripotent precursor cells differentiate into non-dividing neuroblasts and glioblasts that further mature into specialized neuronal and glial cell types - Stem → precursor → blast → specialized - Synaptogenesis: formation of synapses between neurons - Growth of axons, dendrites, synapses; extension of filopodia from growth cones - Growth cone at tip attached to tissue - Extension and contraction of filopodial structures from growth cone - Chemoaffinity: postsynaptic target releases chemical signals that attracts growing axon to appropriate destinations - Dissociated neurons can innervate appropriate targets in vitro - Regrowing frog RGCs will innervate original targets - Netrins identified - Fasciculation – process where pioneer growth cones guide subsequent axons – essential for establishing proper neural pathways - Pioneer growth cones interact with NCAMs that guide along length of path - Apoptosis: programmed cell death; eliminate excess neurons - Cellular shrinkage, chromatin condensation, formation of apoptotic bodies (phagocytized to prevent inflammation) - Early exuberant proliferation, then apoptosis - Cells that do not contact appropriate target under apoptosis - Phagocytosis triggered by surface expression of death signals - Prevents release of individual cellular contents, immune response is not elicited - Glial cells can undergo apoptosis - End career of progenitor cells - Lack of growth factor inhibits expression of Bcl-2 - CA2+ influx and intracellular Ca2+ release activates mitochondrial release of Diablo Fine tuning/Environmental influences  - Synaptic rearrangement: fine tuning; refines neural connections - Spontaneous activity in neurons - Results in more focused pattern of synaptic contact: peak density around 1 yrs old - Topographic gradients – maintain integrity of neuronal map is maintained from source to target - Adjustments made as source and target grow at different rates - Organized by chemical gradients - Waves of activity caused by waves - Open spaces on postsynaptic neurons are filled by sprouting axon terminals of surviving neurons - Synapse survival is competitive - Myelination: process of forming myelin sheath around axons – increases speed of electrical signals between neurons - Commences around 24 weeks after conception - Commences in spinal cord, spread to hindbrain, midbrain, and forebrain - Intense phase of myelination in early postnatal period - Visual depreciation → fewer synapses and spines in PVC - Can result in impaired depth and pattern perception (highlight role of exp in shaping neural architecture) - Devp of lang abilities correlates with synaptogenesis and myelination in Broca’s area Neurulation and Neural development - Neurulation – process that neural plate forms and folds to create neural tube – develop into central nervous system (CNS) - Dorsal epithelial layer (ectoderm) thickens to form neural plate - Neural plate begins to form around day 18 of embryonic development – neural groove appears shortly after - Folds to form neural groove and neural tube and ultimately CNS - Cranial = top; caudal = spinal (bottom) - Days 22-24: lips of neural groove fuse to form neural tube – marks critical step in CNS development - Dorsal epithelial layer (ectoderm): thickens to form neural plate (essential for formation of brain and spinal cord - Neural crest cells – break off from neural tube and migrate to from PNS - Directed by chemical signals - Differentiation of neural crest cells from biochemical signaling during migration - Sensory organs arise (partly) from sensory placodes Cell patterning and specialization - As neural tube closes, constrictions appear – divides developing brain into forbrain, midbrain and hindbrain regions  - Rhombomeres – segmented structures in hindbrain anlage that play role in organization and patterning of neural tissues - Cells at each of the rhombomeres send different signals - Cell patterning occurs in predictable manner; region-specific cells produced at designated times and locations; influence overall architecture of brain - Fine tuned later by apoptosis, synapse rearrangement (original pattering is highly precise) - Sensory organs arise from sensory placodes – specialized regions of ectoderm that contribute to development of sensory systems - Differentiation of neural crest cells is influenced by biochemical signals during migration leading to formation of various neural structures Environmental Enrichment – conditions that provide sensory, social, and cognitive stimulation → enhanced brain development - Crucial for development of neural structures (young organisms) Visual enrichment → structural changes in brain - Thicker cortex, inc dendritic branching, higher number of synapses → enhances neural connectivity and processing capabilities - Organization of visual cortex is significantly influenced by experience (esp during critical periods of devp) - Massive changes in synaptogenesis and myelination of Broca’s speech area → easier to learn languages when younger than older - Monocular deprivation – one eye is deprived of visual input, disrupts ocular dominance columns in primary visual cortex (PVC) - Particularly in layer 4 – demonstrate competitive nature of synaptic connections during development - Sensitive period for visual development begins around 3wks old and close around 6wks - Limited timeframe for optimal visual experience to shape neural architecture - After 1 yr old: effects of monocular deprivation are significantly diminished Environmental Impoverishment – lack of stimulation → detrimental effects on brain development - Minimal sensory input, social isolation, limited opportunities for exploration - Reduced neural connectivity and cognitive deficits - Visual deprivation: fewer eynapses and spines in PVC → impaired visual processing - Deficits in depth and pattern perception – common in individuals exposed to impoverished environments Epigenetics – how behaviors and env can cause changes in gene - Human genome = 20,000 genes - DNA methylation – addition of methyl groups to adenine or cytosine bases → stable decreases in gene expression during cell division and differentiation - Crucial during embryonic development  - Genomic imprinting and X-chromosome inactivation, affects gene expression patterns in a sex-specific manner - Mature cells: methylation of cytosine (particularly CpG dinucleotides) can suppress gene expression by interfering with transcription processes or recruiting specific binding proteins - Histone acetylation modifies tightness of DNA coiling around histones - influences accessibility of DNA for transcription with changes that can persist throughout individual’s lifetime - Interplay between DNA methylation and histone modification is essential for regulating gene expression in response to env stimuli Sensitive Periods and Behavioral Outcomes - Research on rats → maternal care during first week of life can shape temperament of offspring - attentive mothers → reduced fearfulness and more adaptive stress responses - Cross-fostering exp: effects of maternal care can be reversed (emphasize role of env in shaping behavior and stress resilience - Hippocampus of offspring of attentive mothers → decreased methylation of glucocorticoid receptor (GR) promoter and increased histone acetylation lead to higher GR expression (associated with better stress regulation - Methylation patterns established during early devp can persist into adulthood - Influence long-term behavioral outcomes and stress responses Developmental disorders - Fragile X: more severe in boys - CGG repeats causing methylation of FMR1 gene → silence FMRP - Intellectual disability - Phenylketonuria (PKU): increases levels of phenylalanine in blood - Dietary control should not be relaxed after age 2 - Can damage brain/nervous system → learning disabilities Ongoing Neurogenesis – continues in certain brain regions (hippocampus) throughout life; allow for learning and memory - Factors such as exercise, enriched env, and social interactions can enhance neurogenesis in adults - Decline in neurogenesis with age is associated with cognitive decline and memory impairments Age related cognitive decline - Age-associated Memory Impairment (AAMI) – common condition in older adults characterized by mild memory problems that don't significantly interfere with daily life - NIMH criteria: memory performance on at least 1 test measure at least 1 SD below performance for healthy young - Vascular dementia – type of dementia caused by reduced blood flow to brain; often resulting from strokes or other vascular issues  - Stress – chronic stress can negatively impact brain health – lead to neurodegeneration and cognitive decline - Chronically elevated glucocorticoids in stress, Cushing’s disease, major depressive disorder, or glucocorticoid therapy - Alzheimer’s disease – progressive neurodegenerative disorder characterized by memory loss, cognitive decline, and behavioral changes, with significant impacts on aging population - Affects 10% of 65+ and 25% of 85+ - Early stages: preserved distant memory, but impaired consolidation of new declarative memories - Medial temporal lobe function - Impairments in identifying word meaning, uses for common objects, meaning of numbers - End stage: mute/severely disabled - Presence of amyloid beta-containing plaques and neurofibrillary tangles → disrupt neuronal function and communication - Neurofibrillary tangles – pairs of twisted hyper-phosphorylated tau filaments with highly regular periodcity - Genetics: amyloid precursor protein and presenilin genes - Apolipoprotein E (ApoE) gene – implicated in late-onset AD with ApoE4 allele significantly increasing risk of developing disease Aging: ongoing neurogenesis, migration, and learning - Neurogenesis continues in hippocampus, caudate nucleus, olfactory bulb and some other brain regions - BrdU labeling studies → neurogenesis is associated with learning and memory (evi eyeblink conditions in rats) - Survival of new neurons is enhanced in trained rats compared to untrained controls - Aging associated with decline in neurogenesis → cognitive impairments in older adults - AAMI: encompasses spectrum of cognitive decline (mild to dementia) - AAMI varies from mild cognitive impairment to profound dementia - 4.6-38.4% of individuals over 65 exp AAMI - Specific cognitive functions (long-term/working memory) declining; vocab skills remain stable - Aging factors that correlate with AAMI - Intellectual profession and advanced education may be protective - Mood state cluster strongly correlates with cognitive decline - Depression history trait does not correlate strongly, may promote decline in patients with active depression - Treatment for depression in elderly may improve cognitive function Key developmental process  - Devp of nervous system = 7 key processes: - Neurogenesis, production of new cells - Migration, movement to final location - Differentiation, modifications to neuronal/glial type - Synaptogenesis, growth of axons/dendrites/synapses - Apoptosis, programmed cell death - Synaptic rearrangement, fine tuning - Myelination, formation of myelin sheath (not all neurons) - Timing and rate of processes can vary significantly across different regions of developing nervous system Timeline of development - Developmental milestones occur at specific time points - Neurogenesis begins around 7 wks in humans - Anterior pole of neural tube shows swellings by 24-40 days - early brain structure formation - Myelination begins around 24 weeks after conception – critical phase in maturation of nervous system Housing conditions - Lab standard housing: minimal stimulation → hinder brain devp - Enriched housing: variety of stimuli → promote neural growth and cognitive abilities Chapter 8: Sensory Processing and Somatosensation Five senses: - Each system = various sensory receptors organized in distinct hierarchical neural pathways (extract and integrate features of stimuli) - Vision (sight) - Audition (hearing) - Somatosensory (touch) - Pressure, temperature, pain, proprioception - Gustatory (taste) - Olfactory (smell) - Vestibular (balance) Stimulus Salience and perception: - Umwelt: species-specific perceptual world – varies significantly between different species - Salience – (prominence) determined by brain processing – important modalities occupy larger regions of brain; enhance perceptual prominence - Ex. Social odor recognition – prevalent in many mammals but not humans Sensation vs Perception - Sensation – detection of stimulus and recognition that an event has occurred - Constructed differently among differing species - Perception – interpretation and appreciation of sensory stimulus - Influenced by evolutionary adaptations Doctrine of Specific Nerve Energies - Johannes Muller - Each sensory input to brain utilizes different nerve energies - lead to specific perceptions - Brain is functionally divided, with specific conveying distinct types of info - All sensory info is ultimately encoded as action potentials in labelled lines - active neurons determine type of sensation experienced Sensory receptors - Specialized neurons that detect specific physical stimuli (light, sound, pressure) - Most sensory receptors lack axons; cell bodies synapse on dendrites or cell bodies of other neurons - Ex. auditory hair cells (hearing), Pacinian corpuscles (touch), nociceptors (pain) - Three types of sensory receptors: - Free nerve endings – nociceptor (pain/heat) - Enclosed nerve ending – Pacinian corpuscle (touch) - Specialized receptor cell – auditory hair cells (hearing) Stages of Sensation - Reception – (stimulus to receptor) physical energy is absorbed by sensory receptor - Transduction – (receptor to neuron) conversion of physical energy to electrochemical pattern in neurons allow for signal transmission - Coding – (neuron to brain) process where relationship between physical stimuli and action potential is established; enable brain to interpret sensory info Organization of Sensory Inputs - Sensory systems organized topographically – spatial arrangements of sensory inputs correspond to specific areas in brain - Receptive fields help define sensory inputs - larger fields in less sensitive systems and smaller fields in more sensitive systems - Stimulus localization, movement, and direction of movement can be processed by comparing inputs of multiple receptive field inputs - Limited by spatial organization of inputs - Lateral inhibition – enhances sensory acuity by sharpening perception of stimuli - Lateral neurons (close neurons) have decreased action potential → primary neuron has greater effect - Most sensory info is relayed thru thalamus to appropriate cortical circuits - Hierarchical processing – successive levels of processing extract more and more complex attributes of stimulus properties Encoding Stimulus intensity - Intensity can be encoded by specific active neurons and frequency of action potentials - Limited by limited frequency of firing of a neuron - Ability to discriminate intensity is often greater than what can be explained by firing frequency of individual neurons (ex. hearing/vision) - Neuronal assemblies can work tgt, w different neurons recruited at higher intensities; allow for a more nuanced encoding of intensity - Number of active cells → Intensity - Fractionate range of intensity into smaller ranges encoded by specialized neurons Encoding stimulus frequency - Frequency is similarly encoded by active neurons and frequency of action potentials they produce - Limited by limited frequency of firing a neuron - Limitations of neuronal firing frequency can affect how frequency is perceived, necessitating involvement of multiple neurons for accurate representation Adaptation - Tonic receptors – slow/no adaptation, maintain consistent responses to stimuli  - Phasic receptors adapt rapidly, lead to shift in perception/neural activity over time - very active at the onset of stimulation, but they adapt in presence of ongoing stimulation - Sensory systems can modulate responses thru descending inputs (ex. Opioid analgesia) Experience Dependent Plasticity - Plasticity – topographical organization of somatosensory maps (can change based on exp) - Study w monkeys – after extensive training to grasp a spinning disk, cortical representation of hand’s sensory input reorganized to reflect greater sensitivity in trained digits - Sensory processing can adapt based on behavioral demands and exps Somatosensation: touch and pain - Epicritic touch (and Kinesthesia) – mechanoreceptors for fine and discriminative touch sensations - Proprioception - Dorsal column medial lemniscal pathway - Protopathic touch – associated with non-discriminative sensations - pain and temperature - Free nerve endings – responsive to tissue damage, release K+ from nerve - Key receptors: - Pacinian corpuscles (sudden, deep pressure) - Meissner corpuscles (sudden, light touch) - Ruffini corpuscles (gradual, stretch) - Merkel’s disks (gradual, light touch) - Proprioceptors (muscle spindles, GTOs, joint proprioceptors) - Spinothalamic pathway Pathways of Somatosensation - Dorsal column-medial lemniscal pathway – responsible for transmitting epicritic touch sensations - Spinothalamic pathway – transmits protopathic sensations (pain/temperature) - Free nerve endings crucial for detecting tissue damage and are responsive to various chemical signals released during injury Pain processing and Analgesia - Ascending pain fibers release substances like substance P (plays a role in pain transmission) - Analgesia – inability to feel pain - mediated by descending projections from areas such as PAG and raphe nuclei (inhibit pain signals) - Opiate drug mimic descending analgesic actions - Pain may also sensitize (inflammation, neuralgia)  Concept Epicritic Touch Protopathic Touch Sensation Fine, discriminative touch Nondiscriminative touch, pain, Type temperature Receptors Mechanoreceptors (e.g., Meissner, Free nerve endings Merkel, Pacinian) Pathway Dorsal column medial lemniscal Spinothalamic pathway pathway Function High spatial resolution Broad, less precise  Chapter 10: Vision The Visual Stimulus The Anatomy of the Visual System Coding of Light and Dark Coding of Color The Primary Visual Cortex Perception of Visual Information Visual Stimulus - Visible light = 380 to 760 nm (small portion of entire electromagnetic spectrum) - Human eye not sensitive to electromagnetic radiation outside range - Honeybees can detect ultraviolet radiation – allows to see patterns on flowers invisible to humans - Light = particle and wave characteristics Color, Purity, and Brightness - Speed of light: constant at 186,000 miles per second - Frequency of light waves determines wavelength - Longer wavelengths strike surfaces less frequently - Shorter wavelengths strike more frequently - Mixture of all wavelengths produce white light - Single wavelength → saturated color - Intensity of lightwaves influences our perception of brightness - Higher magnitudes = brighter Anatomy of the Visual System Structure of Human Eye - Light travels in straight lines and amount of light entering eye is controlled by iris and pupil - Iris – regulating light intake - dilates = sympathetic stimulation - constricts = parasympathetic stimulation - Lens – focuses light onto retina, create inverted image - Ciliary muscles - Fovea – rich in cones, mediates high acuity and color vision  - Optic disk (blind spot) – area w/o photoreceptors where optic nerve exits eye Types of Eye movement - Vergence movements – allow both eyes to fixate on a target, ensuring proper depth perception - Saccadic movements – rapid shifts of gaze from one point to another, essential for scanning the environment - Pursuit movements – smooth tracking movements that keep a moving object in focus Retinal Processing and Pathways - Retinal Ganglion Cells (RGCs) - Human retina contains approx 120 mil rods and 6 mil cones, which synapse onto 1 mil bipolar cells - Bipolar cells – connect to RGCs (axons form optic nerve) transmit visual info to brain - Types of RGCs: - Parvocellular – (P cell/midget cell) - Small cell body, small receptive field - Sensitive to color/detail - Synapse on parvocellular cells of LGN - Magnocellular (M cells) - Larger cell bodies, large receptive fields - Not sensitive to color/detail - Respond best to moving stimuli - Important for brightness and depth perception - Bistratified cells - 8-10% of RGCs - Inputs from rods, cones, and amacrine cells - Synapse on koniocellular cells of LGN - Photosensitive RGCs - 1-3% of RGCs - Giant cells containing melanopsin - sluggish, long term responses Visual Pathways to Brain - Optic nerves from both eyes converge at optic chiasm (where some fibers cross to opposite side of brain) - Optic nerves project to the dorsal lateral geniculate nucleus (LGN) of the thalamus - Relays information to the primary visual cortex (PVC) - Parvocellular pathway – responsible for color and detail  - Magnocellular pathway – for motion detection and depth perception Perception of Visual Information Dorsal and Ventral Streams - Dorsal stream (magnocellular) – processes spatial awareness and motion - “Where” pathway - Ventral stream (parvocellular) – involved in object recognition and identification - “What” pathway - Allow for comprehensive understanding of visual stimuli, integrate motion and form Retino-suprachiasmatic-hypothalamic pathway – regulates circadian rhythms and synchronizing daily activity cycles (diurnal activity cycles) Hierarchical Processing and Orientation Selectivity - Magnocellular pathway → info about orientation/movement to area V1 of PVC (essential for visual perception) - Simple cortical cells respond to lines positioned within receptive fields (response varying based on lines orientation) - Optimal orientation for each simple cell varies (some cells responding best to vertical lines and others ot horizontal or oblique lines) - Simple cells receptive fields are influenced by inputs from LGN (helps determine orientation selectivity - Complex cells in PVC receive input from simple cells and exhibit orientation selectivity w/o center/surround organization, allow for more complex visual processing Coding of Light and Dark Spatial frequency and motion detection - Spatial frequency – contrast patterns of light and dark in visual stimuli - Analyzed as eyes move (even when fixated on an object) - Eyes are in constant motion → perception of high and low spatial frequency - Motion detection – primarily processed in middle temporal lobe (area MT or V5) - Cells respond specifically to movement direction and speed, independent of other stimulus attributes - Medial superior temporal cortex (MST) – analyze complex motion (circular/spiral movements) - Stabilizes visual images during head and eye movements Retino-Tectal Pathway – crucial for coordinating eye movements, controlling iris muscles (pupil size), regulating ciliary muscles (lens shape for focus) - Integrates visual info w motor responses – allow for quick reflexive actions in response to visual stimuli - Orients gaze towards stimuli – enhance visual attention and perception - Part of broader visual system – includes various neural structures that process visual info before it reaches cortex Stages of Visual Info Processing – convert light into form that brain can interpret → visual perception - Reception - Photoreceptors (rods/cones) constrain numerous lamellae (thin membrane plates essential for light absorption) - Each lamella = approx 10 mil molecules of photopigment (crucial for detecting light) - Photopigments = opsin (protein) and 11-cis retinal (a chromophore) - Rods contain rhodopsin and cones contain iodopsin - Specialized for different light conditions - Mechanism: - Light hits photopigment → cause chemical change → splits opsin from retinal → initiate visual process - Transduction - In darkness – (at rest) cation channels (Na+ and Ca2+) remain open – maintain a depolarized state in photoreceptors - Photoreceptors continuously release neurotransmitter at rest (in dark) - Exposed to light – photopigment undergoes a conformational change, leading to closure of channels and hyperpolarization of cell  - Hyperpolarization → graded decrease in release of neurotransmitter glutamate (alters signal to bipolar cells) In dark In light - Photopigments inactive - Photopigment molecules absorb - Na+ channels held open by CGMP photon and activate - Na+ enters photoreceptor partially - Transducin → phosphodiesterase depolarizing it → breaks down cGMP → Na+ - Photoreceptor continuously channels close releases glutamate - Na+ cannot enter → receptor is hyperpolarized - Glutamate release diminished - Coding - Signal transmission to ganglion cells - Photoreceptors and bipolar cells generate graded potentials (not action potentials), which are only produced by RGCs - Photoreceptors → retinal bipolar cells → retinal ganglion cells - Interaction between photoreceptors and bipolar cells determines response of RGCs – can be excitatory or inhibitory based on type of bipolar cell involved - RGCs – have receptive fields defined as areas of visual field that influences activity - ON cells: excited by light in center - OFF cells: inhibited by light in center - ON/OFF cells: respond to changes in light intensity - Interneurons - Horizontal cells provide lateral inhibition → enhance contrast in visual signals by inhibiting surrounding photoreceptors - Amacrine cells (diverse functions) contribute to processing of visual information (including direction selectivity, on-off) - Bipolar cells can either be hyperpolarized or depolarized by glutamate Coding of Color Cones and color vision - Humans and some primates possess 3 types of cones (sensitive to diff wavelengths of light → color vision) - Presence of 3 iodopsin in cones provides sophisticated mechanism for color discrimination (most advanced in animal kingdom) Color vision - Crucial for various survival functions (discern details in environment)  - Evolution of color vision linked to ecological demands (foraging and social signaling) - 3 types of cones (iodopsin) = trichromatic vision (2nd most complex in animal kingdom) - Sensitive to different wavelengths: short (blue), medium (green), long (red) Trichromatic Theory – (Young-Helmholtz) color perception arises from combination of signals from three types of cones → creation of any color by mixing red, green, and blue light Opponent Process Theory – color perception is controlled by opposing pairs of colors (R/G, B/Y) - Explains negative afterimages that trichromatic theory cannot Retinal Color Coding - Specific responses from cones to diff wavelengths of light → specific ganglion cells process signals → perception of colors - Long wavelengths cones - most responsive to red light - Medium wavelength cones - most responsive to green light - Short wavelength cones - most responsive to blue light Primary Visual Cortex Primary visual cortex (PVC) – located in occipital lobe, responsible for processing visual info from retina - 4 key aspects of visual stimuli: location in visual field, color, ocular dominance, orientation - LGN – relay station, provides organized input to PVC (crucial for visual perception) Color Processing - Parvocellular circuits – in PVC, process input from medium and long wavelength cones - primarily responsible for color perception - Koniocellular circuits – process information from short wavelength cones - contribute to blue color perception and red-green opposition - Color sensitive cells in PVC send info to higher visual areas (V2 and V4), important for color constancy Visual Processing Pathways - PVC exhibits retinotopic organization (adjacent areas of visual field are processed by adjacent areas of cortex) - Interblob regions of V1 contribute to processing ocular dominance and orientation - Blobs involved in color processing Ocular dominance – preference of one eye over the other in visual processing  - An electrode advanced perpendicularly thru interblob column of cortex - All neurons exhibit similar response properties - Most neurons in PVC = binocular (receive input from both eyes) - Often respond more vigorously to one eye’s input than other - Structured organization of ocular dominance columns - Tangential electrode → systematic changes in cellular properties - Ocular dominance can shift → plasticity of visual processing in cortex Orientation sensitivity – neurons respond preferentially to specific orientations of visual stimuli - Neurons in PVC can be categorized based based on maximal response to vertical, horizontal, or oblique lines - Each orientation-sensitive cell has a tuning curve that defines response to various orientations (sharp/broad) - Perpendicular electrode thru interblob column → similar orientation sensitivities - Tangential advancement → smooth transition in orientation preferences Dorsal Stream – (primarily magnocellular) responsible for processing spatial location and movement toward objects - “Where” pathway - Bidirectional signaling and shortcuts between areas - Ex. V1 → V2 → V3 → MT → MST - Motion detection is constructed in brain with specific areas dedicated to analyzing motion direction and speed Ventral stream – (primarily parvocellular) crucial for object recognition, color vision, and identifying forms and features of objects - “What” pathway - Recognition becomes more complex at higher levels of ventral stream - Posterior areas processing general info about objects and anterior areas focusing on individual recognition (ex. faces) - Specific regions within ventral stream dedicated to recognizing specific classes of objects (fusiform cortex for facial recognition and extrastriate body area (EBA) for body parts) Retino Geniculo Cortical Pathway – critical for visual info from retina to visual cortex - Visual processing in primate cortex - Over 50% of primate cortex is implicated in visual processing and associated functions - Facilitate processing of visual stimuli