Cortex 1
There are how many layers of neurons in the neocortex?
There are 6 layers in the neocortex
Which layer of cortex receives most of the input from other brain regions?
In the six-layered neocortex, Layer IV (the internal granular layer) is the main recipient of sensory input from the thalamus
Describe the flow of visual information from the retina to the brain: which cells connect in sequence, what nerve is formed from their axons, where visual information crosses hemispheres, and what thalamic structure sends information to V1.
Flow of information:
Photoreceptors → bipolar cells → ganglion cells
Ganglion cell axons: form the optic nerve
Where visual fields split hemispherically: At the optic chiasm
Thalamic relay structure: Lateral Geniculate Nucleus (LGN), sends projections to V1 (primary visual cortex)
The perception of pitch corresponds to what physical property of sound medium oscillations?
Frequency of sound waves
What is the volley principle?
a theory in auditory physiology that explains how the brain can perceive pitches higher than a single neuron's maximum firing rate
The basic unit of computation in the neocortex is thought to be what?
the vertical array or column of neurons
What is the difference between lateral inhibition and lateral excitation?
Lateral inhibition suppresses the activity of neighboring neurons, which enhances the contrast of a stimulus
Ex.) In vision, when a bright light hits a receptor, it sends signals to inhibit the receptors next to it. This sharpens the perceived edge of the bright object, making it stand out more clearly against the background
Lateral excitation increases the activity of neighboring neurons, which can amplify a signal
e.g.) In the olfactory bulb, lateral excitation across glomeruli can alter odor representations and strengthen the signal when odors are mixed.
After V1, what are the dorsal (“where/how”) and ventral (“what”) pathways responsible for? Is this the only pathway out of the retina, and what condition demonstrates unconscious visual processing?
Ventral pathway ("what"): Processes object identity (temporal lobe)
Dorsal pathway ("where/how"): Processes motion and spatial location (parietal lobe)
Not the only path: True – there are other subcortical pathways (e.g., retina → superior colliculus)
Condition showing unconscious vision: Blindsight – people respond to visual stimuli without conscious awareness
The perception of loudness corresponds mainly to what physical property of sound medium oscillations?
Amplitude
The range of frequencies that will cause a change in the firing rate of an auditory receptor cell is called
characteristic frequency (CF): This is the frequency at which the cell is most sensitive and requires the lowest intensity to cause a response
What are the three principles of connectivity in the neocortex?
One-to-one: One neuron connects to one other neuron
neuron downstream.
2. Divergent: one neuron connects to many others
downstream.
3 . Convergent: many neurons connect to a single neuron.
What are Brodmann’s areas?
regions of the cerebral cortex that Korbinian Brodmann defined in the early 20th century based on their distinct cellular structure, or cytoarchitecture
1.)What is a receptive field, what are retinotopic maps and cortical magnification?
2.) What types of edge detectors exist in V1?
3.)What are orientation and ocular dominance columns, and how are they organized?
1.) A receptive field is the area of the visual field that affects a neuron’s firing.
Retinotopic mapping: Nearby areas in visual space are represented by nearby neurons in the retina, LGN, and V1.
Cortical magnification: The fovea (small area of vision) gets a disproportionately large amount of cortical space.
2.) Edge detectors in V1:
Simple cells: respond to oriented lines in specific positions
Complex cells: respond to oriented lines moving in a direction
End-stopped cells: detect line length or corners
Columns:
Orientation columns: each responds to a specific edge orientation; adjacent columns prefer slightly rotated orientations
Ocular dominance columns: alternate input from left and right eye
Hypercolumn: a full set of orientation columns for both eyes in one functional unit
The cells that transduce basilar membrane vibrations into neural impulses in the ear are called what?
hair cells
Auditory information from each ear projects mainly to _____A._________ primary auditory cortex,
although a small signal remains _____B._______.
A: contralateral primary auditory cortex
B: ipsilateral (same side)
What is the difference between intralaminar and interlaminar projection?
Intralaminar projection refers to neuronal connections that are confined to a single layer (lamina) within a brain structure.
Interlaminar projection describes connections that extend between different layers of a structure.
Vision:
Why do we have greater acuity in our central vision?
because the fovea, the central part of the retina, is densely packed with a high concentration of cone cells
What are saccades, fixations, smooth pursuit movements, the vestibulo-ocular reflex, and the reflexive movement triggered by sudden changes in the visual field?
Saccades: Rapid ballistic eye movements to shift gaze
Fixations: Pauses between saccades where visual information is taken in
Smooth pursuit movements: Track moving objects; require an external visual stimulus
Vestibulo-ocular reflex (VOR): Keeps eyes stable while the head moves
Optokinetic reflex: Eyes follow large moving scenes automatically to stabilize vision
1.)There are believed to be how many different types of these auditory transducers in the ear?
2.)What are they called?
3.)What type of information is each type thought to be responsible for?
1. There are two types of auditory transducers in the ear
2.)inner hair cells and outer hair cells
3.) Inner hair cells: These are the main auditory receptors responsible for sending sound information to the brain.
Outer Hair Cells: These cells mechanically amplify low-level sound entering the cochlea and fine-tune incoming sound waves.
Primary auditory cortex is located in the __A._________ lobe, on ____B._______ gyrus.
A.) temporal lobe
B.) superior temporal gyrus (also known as Heschl's gyrus)
What is distal and local projection in the neocortex?
Local projections are connections within the same or nearby cortical areas
Distal projections are long-range connections to distant regions of the brain.
1.) What is the layered structure at the back of the eye where light is transduced?
2.) How do rods and cones differ in function?
1.) Retina – a 3-layer sheet of neurons that transduces light
2.) Rods – more numerous in the periphery, high sensitivity (night vision), low acuity, no color
Cones – more numerous in the fovea, high acuity, responsible for color vision, need bright light]
What photoreceptors enable color vision, how many types are there, what theories explain color vision (trichromatic vs opponent-process), what opponent color pairs exist, what happens when one is activated, what visual phenomena these theories explain, and what are the conditions of color blindness (insensitivity vs blindness to red/green), as well as what Mach bands help with?
Photoreceptors for color: Cones
Number of cone types: 3 (red, green, blue wavelengths)
Theory supported: Trichromatic theory (Young-Helmholtz)
Explains: Color matching & color blindness
Second theory: Opponent-process theory (Hering)
Explains: Afterimages and opposing color perceptions
Physiological evidence: Yes – LGN and retinal ganglion cells respond in opponent fashion
Opponent color pairs: Red–Green, Blue–Yellow, Black–White
Opponent response: If firing increases to one color, it decreases to the opponent color
Color deficiencies:
Protanomaly – insensitivity to red
Deuteranomaly – insensitivity to green
Protanopia – blindness to red
Deuteranopia – blindness to green
Mach bands function: Enhance edge detection using lateral inhibition
According to the place theory of frequency coding, our perception of different pitches depends on what
aspect of basilar membrane vibration?
High-frequency sounds: Stimulate hair cells at the BASE of the basilar membrane, near the oval window.
Low-frequency sounds: Stimulate hair cells at the TIP (apex) of the basilar membrane.
What is a tonotopy?
The orderly mapping of sound frequency to a specific place in the auditory system, starting in the cochlea and extending through the brainstem and auditory cortex