Biopsychology Session 2 Lectures 5-7

Biopsychology: Vision

• The process of vision involves:
  • Light entering through the pupil and being focused by the lens and cornea
  • Projection of light onto the retina
  • Recognition of different wavelengths by photoreceptors
  • Activation of bipolar and ganglion cells
  • Refinement of the image by amacrine cells and horizontal cells
• The fovea is specialized for detail because each photoreceptor is connected to one bipolar cell, which is connected to a single midget ganglion cell
• The blind spot is where the optic nerve leaves the retina, but it is compensated for by the other eye

Photoreceptors

• There are two types of photoreceptors: rods and cones
• Rods are found throughout the retina, while cones are only found in the fovea
• Both types of photoreceptors release photopigments when struck by light, modifying receptor sensitivity to different wavelengths

Colour Vision

• There are three theories of colour vision:
  • Trichromatic theory: colour is determined by comparing the response of three types of cones with different wavelength sensitivities
  • Opponent-process theory: colour is perceived in terms of opposites (e.g. blue-yellow, red-green, black-white)
  • Retinex theory: the ability to see colour despite changes in lighting, by comparing visual input with previously encountered information

Anatomy of Visual Processing

• The optic nerve pathway involves:
  • The optic nerve leaving the eye
  • The optic nerve crossing in the optic chiasm
  • The optic nerve traveling to the lateral geniculate nucleus (part of the thalamus)
  • The lateral geniculate nucleus sending information to the visual cortex

Lateral Inhibition

• Lateral inhibition allows for optimal object-background differentiation by:
  • Activating neighbouring neurons to heighten contrast
  • Inhibiting bipolar cells in the middle of the illuminated area
  • Allowing bipolar cells on the border to receive only a slight inhibitory signal

Cells

• There are several types of cells involved in visual processing, including:
  • Photoreceptors: activate bipolar and horizontal cells
  • Bipolar cells: activate ganglion cells
  • Ganglion cells: have a doughnut-shaped receptive field and respond to movement and large patterns
  • Parvocellular neurons: detect details and colour, found near the fovea
  • Magnocellular neurons: respond to movement and large patterns, found throughout the retina
  • Koniocellular neurons: have some colour sensitivity, found throughout the retina

Development of Visual Cortex

• The visual system develops before birth, but requires experience to develop, particularly:
  • Synchronizing activity of neighbouring receptors to form connections with cells
  • Visual-experience for fine-tuning
  • Retinal disparity (discrepancy between left and right eye) for stereoscopic depth perception

Ventral and Dorsal Pathway

• The ventral stream (what pathway) is involved in recognizing objects, while the dorsal stream (how pathway) guides movement with visual input
• Damage to the ventral stream can cause visual agnosia (inability to recognize objects)

Visual Hierarchy

• The visual hierarchy involves:
  • Receptive fields becoming larger and more specialized
  • V1 (primary visual cortex): basic features (such as lines and edges)
  • V2 (secondary visual cortex): patterns
  • V3: colour
  • V4: recognition
  • V5 (middle temporal cortex): motion

Object Recognition

• Most brain areas do not respond more to one object than another, but exceptions include:
  • Parahippocampal cortex: responds more to pictures of places
  • Fusiform gyrus: responds more to faces, and damage in this area can cause prosopagnosia (face blindness)

Mechanical and Chemical Senses

• The auditory system involves:
  • Sound waves differing in amplitude, frequency, and timbre
  • Sound entering at the pinna and traveling through the auditory canal
  • Vibration of the oval window creating motion in the liquid in the cochlea
  • Recognition of different sounds by the auditory cortex### Pitch Perception
• Theories of pitch perception:
  • Place theory: certain hair cells respond to specific frequencies, but limited as individual areas of the basilar membrane cannot vibrate on their own.
  • Frequency theory: the entire basilar membrane vibrates at the same frequency as the sound, but limited for low frequencies.
  • Volley principle: several neural populations fire simultaneously, but out of phase with each other.

Auditory Cortex

• 2 pathways of auditory processing:
  • Pathway to process identity: anterior temporal cortex (ventral stream).
  • Pathway to process location: posterior temporal cortex (dorsal stream).
• Primary auditory cortex (A1): processes complex sounds.
• A2: processes nature sounds.
• Superior temporal cortex: processes motion and is responsible for motion deafness when damaged.

Sound Localization

• Methods for sound localization:
  • Difference in time of arrival.
  • Difference in intensity (shadow of the head).
  • Phase difference between the ears.

Hearing Loss

• Types of hearing loss:
  • Deafness: due to environmental factors (e.g., exposure to loud sounds).
  • Conductive deafness: middle ear unable to send soundwaves to cochlea, usually temporary, and treatable with surgery or implants.
  • Nerve deafness: damage to cochlea, hair cells, or auditory nerve, can be inherited or due to exposure.

Vestibular System

• Responsible for balance and distinguishing between self and external movement.
• Semicircular canals filled with fluid and lined with hair cells.

Somatosensation

• Experience of touch, pressure, pain, itch, temperature, and movement.
• Somatosensory receptors:
  • Pacinian corpuscles: detect vibration and sudden displacement on skin.
  • Merkel's disks: detect light touch.
  • Meissner's corpuscle: detect skin movement and object handling.
  • Ruffini ending: detect skin stretching, movement, and finger position.

Awareness of Touch

• Information in the CNS:
  • Info from the head to the brain via cranial nerves.
  • Touch info from periphery to brain via spinal nerves (dermatome).
• Pain:
  • Same pathway as touch.
  • Starts from bare nerve endings in the skin.
  • Dull pain is slow due to unmyelinated axons.
  • Sharp pain is fast due to myelinated axons.

Pain Relief

• Mechanisms of pain relief:
  • Opioid mechanism: opiates and endorphins bind to receptors in the spinal cord and midbrain.
  • Gate theory: pain differs from time to time, and the body closes the 'gate' for pain with endorphins.
  • Anti-inflammatory drugs: reduce release of chemicals in damaged tissue.
  • Placebo: the mere expectation of pain relief.

Taste

• Taste receptors:
  • 50 receptors for 5 different tastes.
  • Located in papillae.
  • Combination of taste and smell (endopiriform cortex).
• Experience:
  • Adaptation: reduction of taste due to fatigue of receptor.
  • Cross-adaptation: reduction in response to a different taste.
• Taste coding in the brain:
  • Taste nerves go to the nucleus of the tractus solitarius (NTS) in the medulla.
  • To somatosensory cortex for touch.
  • To insula (primary taste cortex).

Olfaction

• Smell:
  • Olfactory cells line the epithelium.
  • Cilia (threadlike dendrites) and metabotropic effects.
  • Info sent to olfactory bulb.
  • Women generally have a better sense of smell.
• Pheromones:
  • Unconsciously affect behavior.
  • Only respond to vomeronasal organ.
  • Synchronize menstrual cycles.

Movement

• Muscle contractions:
  • Muscle control by axon releasing acetylcholine.
  • In neuromuscular junction (synapse motor neuron).
• Types of muscles:
  • Smooth muscles: digestive system.
  • Skeletal/striated muscles: movement of body.
  • Cardiac muscles: heart.
• Aerobic or anaerobic:
  • Slow-twitch fibers: aerobic, do not fatigue, oxygen as energy source.
  • Fast-twitch fibers: anaerobic, create oxygen debt, ATP and glycogen as energy source.

Muscle Proprioceptors

• Proprioceptors:
  • Detects the stretch and tension of muscles.
  • Signals to spinal cord to adjust muscle.
  • Stretch reflex.
• 2 types of proprioceptors:
  • Muscle spindles: located parallel to muscles, respond to stretch, and provide negative feedback.
  • Golgi tendon organs: located in tendons, respond to increase in tension, and inhibit further contraction to prevent damage.

Motor Patterns

• Reflex:
  • Consistent, automatic response to a stimuli.
  • Ballistic (once they occur, they cannot be stopped or corrected).
• Sequential movements:
  • Central pattern generators: neural mechanisms of rhythmic patterns of movement.
  • Motor program: a fixed sequence of movements.

Primary Motor Cortex

• Orders movement outcome.
• Posterior parietal cortex: monitors position of body in environment.
• Supplementary motor cortex: planning, rapid sequence movements, and habits.
• Prefrontal cortex: planning, habits, and stores relevant movement info.
• Premotor cortex: active immediately before movement.

Spinal Cord

• Corticospinal tract: pathway from cerebral cortex to spinal cord.
• Lateral corticospinal tract: axons from primary motor cortex and the red nucleus.
• Medial corticospinal tract: axons from midbrain, tectum, and vestibular nucleus.

Cerebellum

• Balance, coordination, timing of action, and attention.
• Cerebellar cortex:
  • Receives sensory input from spinal cord through cranial nerves.
  • Contains Purkinje cells.
  • Parallel fibers activate Purkinje cells one after another.
  • The more Purkinje cells activated, the longer their inhibitory message.
  • Inhibits nuclei in cerebellum and vestibular nuclei in the brain stem.

Basal Ganglia

• Spontaneous behavior, habits, and reward.
• Striatum (caudate nucleus and putamen):
  • Receives input from cerebral cortex and substantia nigra.
  • Sends info to globus pallidus.
• Globus pallidus:
  • Sends info to thalamus and frontal cortex.
• 2 pathways:
  • Direct pathway: striatum inhibits globus pallidus, further inhibiting the thalamus.
  • Indirect pathway: inhibits competing movements.

Movement Disorders

• Parkinson's disease:
  • Gradual loss of dopamine-releasing axons from the substantia nigra.
  • Less inhibitory input to globus pallidus increases inhibitory signal to thalamus.
  • Symptoms: muscle tremors, slow movement, and difficulty initiating voluntary movements.
  • Treatment options: L-dopa treatment and experimenting with brain implants.
• Huntington's disease:
  • Severe neurological disorder due to damaging protein huntington.
  • Symptoms: jerks, facial twitches, and tremors.
  • Extensive brain damage in basal ganglia and cerebral cortex.
  • Confirmed causal genetic relationship.### Oligodendrocytes and Schwann Cells
• Oligodendrocytes are found within the brain and provide myelin for nerve cells
• Schwann cells provide myelin for peripheral nerve cells
• A single Schwann cell wraps a single segment of a peripheral nerve cell

Neurotransmitters

• Neurotransmitters are secreted from the axon terminal
• Autoreceptors are located on the presynaptic membrane

Lesions

• A sham lesion is required for the control group when performing a lesion
• A key advantage of a reversible lesion is that axons of passage are not affected by reversible procedures and each animal can serve as its own control

Myelination

• Myelination allows for quick and efficient transmission of action potential
• Myelination does not change the height of action potential
• Myelination does not increase the energy requirement of a nerve cell

Action Potential

• Hyperpolarization is when the potential becomes overly negative, usually due to potassium (K+) ions
• If a stimulus reaches -60 mV, no action potential occurs

Receptors

• Ionotropic receptors directly open an ion channel
• Metabotropic receptors use G protein activation to activate a second messenger, leading to a longer-lived effect on ion channels

Brain Structure

• Cerebrospinal fluid is produced within the ventricles
• The parietal lobe is involved in somatosensory function
• The occipital lobe is involved in visual function
• The temporal lobe is involved in auditory function
• The basal ganglia consists of the putamen, globus pallidus, and caudate nucleus, but not the amygdala
• The ventral visual stream projects to the temporal lobe and is involved in object recognition

Auditory System

• The correct order of the auditory system is: auditory canal, eardrum, stirrup, anvil, and hammer, oval window and cochlea, hair cells