Striate Nucleus, Ganglion Cells

Bipolar cells

Second-order retinal neurons that receive photoreceptor input and transmit signals to ganglion cells

Primary role of bipolar cells

Transform and enhance visual signals before transmission to ganglion cells

ON bipolar cells

Sign-inverting bipolar cells that depolarize when photoreceptors hyperpolarize in light

OFF bipolar cells

Sign-conserving bipolar cells that hyperpolarize when photoreceptors hyperpolarize in light

Sign inversion

Response polarity reversal between photoreceptor and postsynaptic neuron

Sign conservation

Response polarity maintained between photoreceptor and postsynaptic neuron

Metabotropic glutamate receptors

Glutamate receptors that mediate ON bipolar cell responses through second messenger pathways

Ionotropic glutamate receptors

Glutamate receptors that mediate OFF bipolar cell responses through direct ion channel activation

AMPA receptors

Fast ionotropic glutamate receptors associated with transient bipolar cell responses

Kainate receptors

Ionotropic glutamate receptors associated with sustained bipolar cell responses

Transient response

Rapid short-lived neural response to stimulus onset or offset

Sustained response

Neural response maintained throughout stimulus presentation

Ribbon synapse

Specialized synapse capable of continuous neurotransmitter release for graded signaling

Graded potential

Continuous change in membrane voltage proportional to stimulus strength

Photocurrent

Light-evoked electrical response generated by a photoreceptor

Dark current

Continuous inward flow of sodium and calcium ions in photoreceptors in darkness

Photoreceptor hyperpolarization

Decrease in membrane potential caused by light-induced closure of outer segment channels

Cone photoreceptors

Photoreceptors specialized for daylight vision color vision and rapid responses

Rod photoreceptors

Photoreceptors specialized for dim-light vision and high sensitivity

Rod-cone sensitivity difference

Rods are more sensitive to light whereas cones respond faster

Rod-cone kinetic difference

Cones have faster response dynamics than rods

Calcium influx in rods

Approximately 15% of rod dark current is carried by calcium ions

Calcium influx in cones

Approximately 35% of cone dark current is carried by calcium ions

Cone bipolar cells

Bipolar cells receiving input from cone photoreceptors

Rod bipolar cells

Bipolar cells receiving input exclusively from rod photoreceptors

Midget bipolar cells

Cone bipolar cells receiving input from a single cone in the fovea and supporting high acuity vision

Diffuse bipolar cells

Cone bipolar cells receiving input from multiple cones and integrating visual information

Blue cone bipolar cells

Bipolar cells specialized for signals originating from S-cones

One cone-one bipolar-one ganglion pathway

Foveal circuit that maximizes spatial resolution through minimal convergence

Signal convergence

Combining input from multiple photoreceptors onto fewer downstream neurons

Low convergence circuitry

Neural organization preserving spatial detail through limited pooling of signals

High convergence circuitry

Neural organization sacrificing spatial resolution to improve sensitivity

Triad synapse

Photoreceptor synapse involving horizontal cells and invaginating bipolar cell contacts

Invaginating synapse

Bipolar cell contact located within the photoreceptor synaptic invagination

Flat synapse

Bipolar cell contact located outside the photoreceptor invagination

Semi-invaginating synapse

Intermediate bipolar cell contact position relative to the synaptic invagination

Outer plexiform layer

Retinal layer containing synapses between photoreceptors bipolar cells and horizontal cells

Contrast encoding

Neural representation of differences in luminance rather than absolute luminance

Contrast gain

Amplification of contrast signals by retinal circuitry

Contrast enhancement

Increase in sensitivity to luminance differences between adjacent regions

Nonlinear signal transfer

Relationship where output is not directly proportional to input

Linear response

System output changes proportionally with input

Contrast sensitivity

Ability to detect small differences in luminance

Weber's law

Principle stating that detectable intensity changes are proportional to background intensity

Delta I over I

Mathematical expression describing Weber's law

Light adaptation

Adjustment of visual sensitivity to changing illumination levels

Intrinsic bipolar adaptation

Adaptive mechanisms within bipolar cells that further enhance contrast processing

Contrast rectification

Preferential amplification of one contrast polarity over another

Temporal filtering

Selective transmission of signals based on timing characteristics

Bipolar cell molecular fingerprint

Unique gene expression profile distinguishing bipolar cell subtypes

Single-cell transcriptomics

Technique used to classify neurons based on gene expression patterns

Retinal cell diversity

Existence of numerous functionally distinct retinal neuron subtypes

Parallel visual pathways

Separate retinal circuits specialized for different aspects of visual processing

Functional specialization

Different neuron classes performing distinct computational tasks

Photoreceptor-bipolar transformation

Conversion of relatively linear photoreceptor signals into enhanced contrast representations

Disease-induced retinal rewiring

Formation of new synaptic connections by bipolar cells following photoreceptor degeneration

Primary visual cortex (V1)

First cortical area receiving visual input from the LGN

Striate cortex

Primary visual cortex characterized by the stria of Gennari

Area V1

Brodmann area 17 and the primary cortical recipient of visual information

Brodmann area 17

Cytoarchitectonic designation for primary visual cortex

Stria of Gennari

Dense band of myelinated axons in layer IV of primary visual cortex

Koniocortex

Cortical region with a highly developed granular layer IV specialized for sensory input

Layer IV of cortex

Primary input layer receiving thalamic projections

Cortical magnification factor

Disproportionately large cortical representation of the central visual field

Foveal magnification

Expansion of central visual information across a large cortical area

Retinotopic organization

Preservation of spatial relationships from retina to cortex

Visual field representation

Mapping of visual space onto cortical tissue

Contralateral representation

Processing of one visual hemifield by the opposite cerebral hemisphere

Calcarine sulcus

Major occipital lobe landmark containing primary visual cortex

Superior visual field representation

Mapped onto the inferior bank of the calcarine sulcus

Inferior visual field representation

Mapped onto the superior bank of the calcarine sulcus

Cytoarchitecture

Organization of neurons and layers within cortical tissue

Gray matter

Cortical tissue containing neuron cell bodies dendrites and synapses

White matter

Brain tissue composed primarily of myelinated axons

Pial surface

Outer surface of the cerebral cortex

White matter border

Boundary between cortical gray matter and underlying axonal tracts

Pyramidal neurons

Principal excitatory output neurons of the cerebral cortex

Glutamate

Primary excitatory neurotransmitter of cortical pyramidal neurons

Spiny stellate cells

Cortical neurons commonly involved in receiving sensory input

Smooth stellate cells

Local inhibitory interneurons lacking dendritic spines

Interneurons

Local circuit neurons that regulate cortical activity

GABA

Primary inhibitory neurotransmitter in the cerebral cortex

Excitation-inhibition balance

Critical regulation of cortical activity through opposing neural influences

Feedback connections

Cortical projections that influence earlier stages of processing

Orientation selectivity

Preference of a neuron for stimuli with a particular orientation

Simple cells

V1 neurons with orientation-selective receptive fields containing distinct ON and OFF regions

Simple cell receptive field

Elongated receptive field with spatially separated excitatory and inhibitory zones

Complex cells

Orientation-selective neurons lacking distinct ON and OFF subregions

Complex cell invariance

Ability to respond to preferred orientations despite changes in exact position

End-stopped cells

Cortical neurons responding strongly to line endings corners and edges

Hypercomplex cells

Older term for end-stopped cells

Hubel and Wiesel model

Theory explaining how cortical receptive fields arise from convergent inputs

Orientation column

Vertical cortical module containing neurons with similar orientation preferences

Cortical column

Functional unit of cortex organized perpendicular to the cortical surface

Ice cube model

Simplified representation of cortical column organization in V1

Ocular dominance columns

Alternating cortical regions receiving dominant input from one eye

Ocular dominance

Relative influence of one eye on cortical neurons

Layer IV ocular dominance columns

Region where eye-specific segregation is most evident

Visual cortex blobs

Cytochrome oxidase-rich regions specialized for color processing

Interblobs

Cortical regions between blobs associated with orientation processing