PSYC 212 - Post-Midterm 2

Phoneme

a unit of sound that distinguishes one word from another in a particular language

• ex: kill vs. kiss are composed of 3 phonemes: "kh" "eih" and "ll" vs. "ss"

- To get around confusing differences between sound and spelling, the International Phonetic Alphabet (IPA) is used

- About 5000 languages are spoken today, utilizing over 850 different speech sounds

Speech Production Process: Respiration, Phonation, Articulation

Respiration: The diaphragm pushes air from the lungs → trachea → larynx.

Phonation: As air passes through the larynx, vocal folds vibrate.

- More tension = higher pitch.

- Smaller vocal folds = higher pitch (e.g., children > women > men).

- Produces a harmonic sound spectrum.

Articulation: The vocal tract (oral + nasal cavities above the larynx) is shaped by the jaws, lips, tongue, and velum to create distinct sounds.

- Changing tract shape/size affects resonance, altering frequency distribution.

- Formants (F1, F2, F3) are key spectral peaks; spacing helps identify phonemes.

- Shorter tracts = higher formant frequencies.

- First 3 formants are usually enough for recognizing speech sounds.

Spectrograms: Visualize speech over time.

- X-axis: time | Y-axis: frequency | Color: amplitude (energy)

Coarticulation

the blending or overlapping of sounds (articulations) in rapid speech

In rapid speech (10-15 consonants/sec), sounds overlap.

Experienced speakers adjust tongue and mouth in advance for upcoming sounds (body preps for the next sound before it’s even fully produced)

McGurk Effect

Occurs when lip movements don’t match spoken sounds, leading to altered perception (key ex. of multisensory perception)

Motor Theory of Speech Perception: We understand speech by mentally simulating how it's produced; the brain uses motor processes in reverse to interpret sounds.

The McGurk Effect (McGurk & MacDonald) supports this: visual input (lip movements) can change what we hear

Criticism: Speech production is as complex, or more so, than perception.

Proposed Solution: Simplify by reducing the number of phonetic categories

Examples of attuning to phonemes in development

Four-day-old French babies prefer French over Russian

In Japanese, 'r' and 'l' have no sound distinction

Infants begin filtering out irrelevant phonemes before even saying speech sounds

English-speaking infants <10 months can distinguish between two types of "t" sounds that are different phonemes in Hindi, but lose that ability after 10 months, while Hindi infants still continue to make the distinction

How Does the Auditory System Resolve Coarticulation?

Coarticulation: Overlapping articulation of phonemes can make sounds ambiguous.

Motor Theory of Speech Perception:

- Suggests we interpret speech by simulating the motor commands used to produce it.

- Visual cues (e.g., lip reading) help disambiguate sounds.

Effect: Narrows down the possible phonemes perceived.

Integrates auditory and visual information to improve accuracy.

Wernicke's area

A region in the left hemisphere of the brain responsible for linking sounds or sound patterns with meaning.

- Lesions in this area impair the ability to understand language and assign meaning to words, even though hearing is intact. Patients may also produce speech that sounds fluent but uses incorrect or nonsensical words.

- This results in Wernicke's aphasia (aka fluent aphasia): speech appears normal in flow and tone but lacks meaningful content, making it difficult to understand.

Broca's area

Located in front of the primary motor cortex (left hemisphere).

Plans the complex movements needed for speech (articulation & coarticulation).

Broca's Aphasia (Non-Fluent Aphasia): patients understand speech but struggle to produce words

- Caused by damage to Broca’s area

Two main functions of music

to cheer up or calm infants and to bring people together

Tone height

a sound quality corresponding to the level of pitch

- Monotonically related to frequency

Tone chroma

A quality of sound that makes notes of the same name (like every "A") across different octaves sound similar.

Each note (A–G) has a unique chroma, repeated every octave.

Shows that musical pitch involves more than just frequency.

Octave

An octave is the interval between two sound frequencies with a 2:1 ratio (ex: 440 Hz and 880 Hz sound one octave apart).

- In Western music, an octave is divided into 12 equal pitch intervals (semitones), creating 13 notes (including the starting and ending note).

- The audible range spans about 10 octaves, and a piano covers 7 of them.

Consonance and Dissonance

Consonance: Notes played together sound pleasant.
- Occurs when their fundamental frequencies have a simple ratio (ex: 3:2), so many harmonics overlap.

Dissonance: Notes played together sound unpleasant or "off."
- Occurs when their frequencies have a complex ratio (ex: 42:33), so few harmonics overlap.

Scales and Key

Scale: a specific set of notes within an octave

- Major and minor scales differ by the pattern of intervals (semitones) between notes.

- Major scales tend to sound happy, minor scales sad.

Key: the scale that forms the foundation of a musical piece.

- For example, music in the key of C major mostly uses notes from the C major scale.

- The tonic is the root note of the key—like a musical "home base" that gives a sense of resolution and rest.

Melody

a sequence of notes or chords perceived as a single coherent structure

- Can be defined by contours (patterns of rises and declines in pitch) rather than by an exact sequence of sound frequencies

- Can change octaves or keys and still be the same melody, even if they have completely different notes

- ex: "twinkle twinkle little star"

Parabelt region of the right auditory cortex

where music is mainly processed

Congenital Amusia & Neural Correlates

Lifelong musical impairment not due to intellectual disability, lack of exposure, or postnatal brain damage.

Deficits:

- Can't detect pitch deviations below 2 semitones.

- Can't report out-of-key tones.

Brain Structure:

- Abnormalities in the right frontotemporal network: inferior frontal gyrus & superior temporal gyrus (STG)

- Impaired connectivity between these areas and the left STG.

ERP Markers in Amusia: ERAN & P600

ERAN (Early Right Anterior Negativity, ~200 ms):

Triggered by unexpected notes in a melody.

- Present in amusics, meaning they unconsciously detect pitch errors.

P600 (~600 ms):

Reflects conscious awareness of tonal violations.

- Absent in amusics, so they detect errors but aren’t aware of them — they’re "in-tune but unaware."

Absolute pitch (AP)

A rare ability (1 in 1,500 people) to identify or produce musical notes without any reference.

Heritability: Higher concordance in monozygotic than dizygotic twins suggests a genetic component.

Environment: Early musical training is likely also necessary for AP to develop.

Descartes

believed humans have immaterial souls and that all sense perception is a dream, he calls sensations of the body passions of the soul

Ian Waterman

lost all tactile sensation and proprioception after a virus and taught himself to walk

Proprioception and Kinesthesia

Proprioception: sense of body position

- Based on the ability to perceive the position of the joints

- Includes vestibular sensations (sense of balance)

Kinesthesia: perception of movement

- Doesn't include balance

- Substantially the same receptors as proprioception

Two main kinds of receptors for the two systems:

- Muscle Spindle: nerve fibers attached to muscle fibers

• function as stretch receptors

- Golgi Tendon Organ: located within tendons as a part of muscle attached to the articulation

• can perceive amount of pull there is on specific tendon

Tactile Perception & Thermalgesia

The sense of external objects touching the skin (exteroceptive sense)

Involves specialized nerve fibers with dendritic endings, including: Pacinian corpuscle, Ruffini’s corpuscle, Meissner’s corpuscle, Merkel’s receptor

Thermalgesia (Temperature & Pain):

• The sense of internal body temperature (interoceptive sense)

• Involves free nerve endings on sensory fibers (no specialized corpuscles)

Tactile receptors with slow vs. fast adaptation rate

Slow adaptation rate: receptor will start firing upon contact with stimulus, it will continue firing as long as the contact is maintained

• Doesn't adapt to presence of stimulus

Fast adaptation rate: receptor will fire upon contact with stimulus, but if contact is maintained with the same force (there's no change), they will adapt and stop firing

Different types of Mechanoreceptors (SA I, SA II, FA I, FE II)

SA I cells: associated with Merkel receptors

- Have small receptive field and have a slow adaptation rate

- Good for perceiving fine-grain patterns of tactile stimulation

SA II cells: only located in hands

- have a larger receptive field and have a slow adaptation rate

- Good for perceiving skin deformations/stretching of skin (good for prepping to grab an object)

FA I fibers: associated with Meissner corpuscles

- Have a fast adaptation rate

- Good for holding grip onto an object (telling if it's sliding away), good at perceiving low-frequency vibrations

FA II fibers: associated with Puccini receptors

- More sensitive than FA1 fibers to high-frequency vibrations but otherwise very similar

Tactile perception

all touch fibers eventually group together into a nerve that enters the spinal cord between each spinal disc

- Dermatoma: Each area of the skin innervated by a specific nerve

Dorsal column pathway

when tactile information enters the spinal cord, it will directly ascend towards the brain by following this pathway

When tactile info enters the spinal cord, it remains on the same side as it entered, then makes the first relay in the brain stem in two different nuclei (Cuneate nucleus and the Gracile nucleus)

After relaying to nuclei, axons cross to the other side and make a second synapse in the ventral posterior nucleus of the thalamus

From there, information reaches the somatosensory cortex (posterior to central sulcus)

Somatotopic organization

every part of the body has a corresponding part in the sensory cortex that will specifically receive information from that part of the body

Two-point discrimination threshold

A test using two pins at varying distances to measure touch sensitivity.

- Participant reports if they feel one point or two.

- If both pins fall within one large receptive field, only one point is perceived.

- Hands and face have more nerve fibers and smaller receptive fields → can detect smaller distances between two points.

- Areas with fewer fibers and larger receptive fields (e.g., back) have higher thresholds — feel two points as one.

More receptors = smaller receptive fields = better spatial resolution.

Pain

an unpleasant sensory and emotional experience associated with or resembling that associated with actual or potential tissue damage

Nociception: the neural process of encoding nociceptive stimuli

Nociceptive stimulus: actual or potentially tissue-damaging event transduced and encoded by nociceptors

Pain Intensity vs. Specificity Theory

Intensity Theory: Pain results from overly intense stimulation of general sensory neurons, no dedicated pain system

- any high-intensity sensation can be perceived as pain

Specificity Theory: Pain is detected by specialized neurons (nociceptors) that respond only to noxious stimuli

- The discovery of nociceptors supports the Specificity Theory.

Opioid Mechanism of Action

Mu-opioid receptors reduce pain (nociception) by acting at both presynaptic and postsynaptic sites:

- Presynaptic inhibition: Blocks Ca²⁺ influx, reducing neurotransmitter release.

- Postsynaptic inhibition: Increases K⁺ efflux, causing hyperpolarization, which lowers the chance of the neuron firing.

Overall effect: Pain signal transmission in the spinal cord is suppressed.

Nociceptors

are there different fiber types? spinal cord transmission?

Sensory receptors that detect harmful or potentially damaging stimuli to the skin

Two fiber types:

A-delta (Aδ) fibers:

• Myelinated, medium-sized

• Transmit fast, sharp pain and temperature

C-fibers:

• Unmyelinated, small

• Transmit slow, throbbing pain and temperature

Two-stage pain response:

1) Quick, sharp pain → A-delta fibers

2) Delayed, throbbing pain → C-fibers

- Speed difference = due to myelination

Spinal cord transmission is bidirectional:

- Pain info ascends to the brain

- Brain can modulate pain signals (descending pathway)

- Brainstem plays a key role in this descending control

Local anesthetics

Local anesthetics block sodium channels, preventing Na⁺ entry and completely stopping the action potential from propagating.

In myelinated fibers, signals can skip over individual nodes of Ranvier, so at least 3 nodes must be blocked to fully stop nerve conduction.

Fiber sensitivity to anesthetics (from least to most sensitive):

- Motor fibers (largest, thickly myelinated)

- Tactile & proprioceptive fibers

- A-delta fibers (nociceptors)

- C-fibers (unmyelinated pain fibers)

Chronic insensitivity to pain

Pain receptors don’t work, so individuals don’t feel pain

Leads to severe injuries, limb loss, and often early death

The full syndrome also includes autonomic nervous system deficits

Limbic touch

Triggered by light, pleasant touch (e.g., feather or soft brush stroking the skin).

Involves a special type of C fibers.

Produces a pleasant emotional response, not just physical sensation.

Nociceptors and Spinal Cord Pathway

Nociceptors first synapse in the dorsal horn of the spinal cord, specifically in laminae 1 or 2.

Most tactile fibers don’t synapse here, but some do.

The second neuron (spinal projection neuron) crosses to the opposite side of the spinal cord and ascends to the thalamus for another synapse.

From the thalamus, the signal moves to the cerebral cortex.

Touch sensation vs Pain information

Touch (Dorsal Column Pathway):
Travels up the same side of the spinal cord (ipsilateral) and crosses over at the brainstem.

Pain & Temperature (Spinothalamic Pathway):
Cross over immediately at the level of spinal cord entry, then ascend on the opposite side to the brain.

Spinothalamic Pathway:
Named for the neuron connecting the spinal cord to the thalamus, central to pain perception

Two types of spinal projection neurons

Spinal projection neurons are the second-order neurons that relay nociceptive signals in the spinal cord

1) Nociceptive-Specific Neurons

- Respond only to painful (noxious) stimuli

- Ignore mild or non-painful input

2) Wide Dynamic Range (WDR) Neurons

- Respond to both non-noxious and noxious stimuli

- Firing rate increases with stimulus intensity

Pattern theories of pain

what matters is the specific pattern of activity across a large population of neurons

Gate Control Theory of Pain

Concept: Gentle touch (like stroking near an injury) can reduce pain by affecting how the spinal cord processes sensory input.

Mechanism

A Transmission (T) neuron in the spinal cord receives signals from:
• C fibers (carry pain)
• A fibers (carry touch)
• SG (substantia gelatinosa) interneuron, which is inhibitory

Touch input activates A fibers, which stimulate the inhibitory SG neuron, effectively “closing the gate” and reducing pain signals sent to the brain.

Activation Scenarios (Pain Modulation)

if only A fibers activated, the SG neuron is activated, which inhibits the T neuron, decreasing pain

if only C fibers activated, the SG neuron is inhibited, which disinhibits the T neuron, increasing pain

if both A & C fibers activated, the SG neuron remains at baseline, and partially inhibits the T neuron, reducing pain (compared to C fibers alone)

Involves wide dynamic range neurons (respond to both A & C fibers)

Clinical Use: TENS (Transcutaneous Electrical Nerve Stimulation) activates A fibers to temporarily reduce pain

Placebo Analgesia and Endogenous Opioids

Tourniquet Test (pain induced by blocking blood flow, over 3 days):

- Day 1: No treatment → baseline pain.

- Day 2: Told they’re getting an opioid, but given saline → pain relief (placebo effect).

- Day 3: Given naloxone (blocks opioid receptors) → no pain relief (placebo effect blocked).

Control Group: Given naloxone without placebo history → no pain relief, proving naloxone doesn’t reduce pain on its own

Conclusion: Placebo analgesia is real and driven by endogenous opioids, which are blocked by naloxone

Referred pain

happens when there are positive signals in an internal organ, you don't feel the pain in that organ, instead, the pain is felt in another seemingly unrelated patch of skin

- Ex: in a heart attack, patient typically feel pain spreading to the index of their left because 1) nociceptive system is bad at location of pain when it happens in an internal organ, 2) information coming from internal organs also enters the spinal cord and species with new susceptive information that is coming from a patch of skin

Spinothalamic vs Dorsal Column Pathways & Brown-Sequard Syndrome

Spinothalamic Pathway (Pain/Temperature)

Crosses to the opposite side immediately at spinal cord entry, then ascends to the thalamus and cortex.

Dorsal Column Pathway (Touch/Pressure)

Ascends on the same side of the spinal cord and crosses over at the brainstem.

Brown-Sequard Syndrome (One-sided spinal cord lesion)

- If lesion is on the right side:
→ Left-side (contralateral) loss of pain/temperature (spinothalamic).
→ Right-side (ipsilateral) loss of touch/pressure (dorsal column).

One spinal lesion causes opposite-side losses for different sensory types — called sensory dissociation.

Conditioned Pain Modulation

Pain in one area (ex: cold water on the left hand) can reduce pain sensitivity elsewhere (ex: heat pain on the right hand)

After the cold stimulus, pain thresholds increase, indicating reduced sensitivity

This effect occurs because ascending pain signals activate the brainstem, which triggers descending inhibitory controls that dampen pain signals throughout the body.

• aka the “pain inhibits pain” phenomenon

Fibromyalgia

A chronic pain disorder marked by widespread musculoskeletal pain, fatigue, "fibro fog" (cognitive issues), and sleep problems.

Caused by abnormal pain processing in the central nervous system (nervous system becomes overly sensitive to pain)

Patients lack descending modulation (natural pain control), shown by feeling the same pain whether sensation builds up (fingers → arm) or fades (arm → fingers)

Exact cause unknown, but central sensitization is a key factor

Emotion and Pain: Nociceptive Flexion Reflex (NFR) Study

NFR: An involuntary spinal reflex triggered by painful stimuli (e.g., heat or pressure), causing limb withdrawal and opposite limb extension (crossed-extension reflex). It is used as an objective measure of spinal pain processing and sensitivity.

Design: Participants viewed emotional or neutral images while receiving electrical foot shocks.

- Unpleasant images → higher pain ratings and increased NFR amplitude

- Pleasant images → lower pain ratings and reduced NFR amplitude

Follow-up Study: Pleasant vs. unpleasant music showed similar effects on pain modulation at the spinal level.

Conclusion: Emotions influence pain perception and spinal reflexes, not just cortical processing.

Dimensions of Pleasure and Reward Processing

Desire/Wanting:

- Pursuit phase of a reward (before obtaining it)

- Driven by dopamine release in the frontal lobe

- Increases motivation and energy to seek rewards

Pleasure/Liking:

- Enjoyment upon receiving reward

- Mediated by opioid release in hedonic hotspots

Motivation-Decision Model of Pain

suggests that the CNS prioritizes stimuli and inhibits pain when something more important is present. In other words, if another stimulus is deemed more urgent, the brain reduces the sensation of pain

- On neurons: Activated by opioid antagonists (ex: naloxone), which increase pain

- Off neurons: Activated by opioids (ex: morphine), which inhibit pain transmission at the spinal cord level

Flow

state of intense focus and absorption in an activity where a person is fully immersed in the task at hand and loses track of time and their surroundings (usually when someone does something they like doing and are particularly good at doing)

Video Games Effect on Pain Tolerance

Playing video games, even non-preferred ones, reduces pain intensity and unpleasantness more than basic tasks like the 2-back or left-right test.

Pain intensity ranking (least to most):
Preferred game < Non-preferred game < 2-back < Left-right

Pain unpleasantness ranking:
Preferred game < Non-preferred game < 2-back < Left-right

Why? Video games create a flow state (dopamine-driven, reward-focused immersion), which distracts from pain.

Music Selection and Pain Perception

Showed that participant-selected (preferred) music is much more efficient at reducing pain compared to experimenter-selected music

Pain vs Nociception

Pain: An unpleasant sensory and emotional experience (subjective feeling - qualia)

Nociception: An objective neural process that encodes a noxious (harmful) stimulus, like detecting potential tissue damage

Nociception can occur without pain, Pain can occur without nociception.

Nociception without pain ex: Stress-induced analgesia (little pain after an accident due to noradrenaline release).

Pain without nociception ex: Phantom limb pain (pain felt in a limb that’s no longer there) or a construction worker feeling severe pain despite an uninjured foot with a nail between the toes.

Melzack's three main dimensions of the multidimensional experience of pain

1) Sensory Dimension: The location, intensity, and qualities of the pain

2) Effective Motivational Component: The urge to act and stop the pain

3) Cognitive & Evaluative Component: The brain processes the meaning of pain, like the cause and what to do about it

Neuro Signature of Pain: Melzack proposed pain is a specific brain activity pattern (neuro signature) that involves the neural matrix, brain regions representing the body

- Thalamus: Receives nociceptive signals

- Somatosensory Cortex (S1, S2), Insula, and ACC: Process sensory and emotional pain aspects

Lesion in primary somatosensory cortex

Leads to a sensory pain deficit:

- Can’t identify or localize pain (loss of sensory dimension)

- Still feel the unpleasantness of pain (emotional dimension remains intact)

Phantom Limb Pain and the Brain

Affects 60–80% of amputees; severe in 5–10%.

Starts within days/weeks after amputation, often intermittent and decreases over time.

Rare in infants, suggesting a role for brain plasticity.

Linked to reorganization in the primary somatosensory cortex—adjacent body parts take over the area for the missing limb, causing phantom sensations and pain.

Functional Reorganization and Mirror Therapy

Reorganization: When a body part is lost, the brain's sensory areas can invade adjacent regions. Stimulation of these areas can trigger sensations in the missing limb, causing confusion.

Mirror Therapy: Uses a mirror to make the brain believe the missing limb is still there, helping reduce reorganization and relieve pain.

Study Results: Mirror therapy is more effective than mental visualization or covered-mirror therapy for reducing pain and promoting brain function.

Related Concept: The rubber hand illusion works only with synchronous stimulation (both the real and fake hand must be stimulated at the same time).

Lesion in the Anterior Cingulate Cortex (ACC)

The individual still perceives pain (via the primary somatosensory cortex) but doesn’t feel its emotional impact, no fear, distress, or sense of danger

This shows the ACC is crucial for the emotional component of pain, not the physical sensation itself

Effect of hypnosis on pain

When using hypnotic suggestions targeting the affected dimension of pain, the anterior cingulate cortex (ACC), pain is reduced

Hypnotic suggestions didn't have any impact on the sensory input (somatosensory) dimension of pain

Neural signatures of pain

Neural Pain Signature (NPS): Predicts how much pain a person is feeling based on brain activity

SIIPS (Stimulus Intensity Independent Pain Signature): Captures changes in perceived pain that aren't explained by stimulus intensity

These signatures help predict pain from brain activity and are used to test whether altering brain activity can change pain perception, though this only works in specific situations

Physical vs chemical senses

Physical Senses:

- Audition (hearing): Pressure waves hit the eardrum, activating hair cells in the inner ear.

- Vision: Photons hit the retina’s rods and cones.

- Touch: Pressure and vibration activate sensory cells in the skin.

Chemical Senses:

- Taste (gustation)

- Smell (olfaction)

- Trigeminal system: Responds to chemical stimuli like those from spicy foods.

Taste Perception and Taste Buds

Taste = interaction of soluble substances with gustatory receptors in taste buds

Five basic tastes: sweet, sour, salty, bitter, umami

Taste buds are located on the tongue’s mucosa and on three types of papillae (Fungiform, Foliate, Circumvallate)

• Filiform papillae are sensory but not involved in taste

All taste qualities can be detected across the entire tongue

Central Pathway of Taste

All taste signals begin in taste buds and follow a common path: tongue area and crainal nerve (see below) → brainstem (solitary nucleus) → VPM of thalamus → primary taste cortex (insula & parietal cortex); some also project to the hypothalamus & amygdala (emotion-related areas)

Anterior 2/3 of tongue → CN VII (7) (Facial)

Posterior 1/3 of tongue → CN IX (9) (Glossopharyngeal)

Epiglottis → CN X (10) (Vagus)

Smell: Structure and Function

how is smell initially detected? approx how many receptors do humans have? what are ORNs?

Smell is detected by olfactory receptors in the olfactory mucosa (upper nasal cavity)

Humans can distinguish billions of odors using ~400 types of olfactory receptors

Olfactory receptor neurons (ORNs):

- Each ORN expresses a single receptor type, located in its cilia

- ORNs can respond to multiple substances, and each substance can activate multiple receptor types, enabling diverse combinations

- ORNs regenerate from stem cells and are supported by surrounding cells

- Their axons pass through cribriform plate and synapse in olfactory bulb

- Axons from ORNs with the same receptor type converge in same glomerulus

Olfactory Pathway and Brain Processing

Olfactory signal travels via two neurons:

1) ORN → Olfactory bulb

2) Olfactory bulb → Primary olfactory cortex

Primary areas: piriform cortex, amygdala, entorhinal cortex.

Secondary areas: orbitofrontal cortex, insula.

Ipsilateral processing (no crossover).

No thalamic relay required (unique among senses).

Olfactory areas overlap with the limbic system — involved in emotion (amygdala), memory (hippocampus, entorhinal), and reward (orbitofrontal cortex).

Types and Functions of Olfaction

Types & Functions of Olfaction

- Orthonasal: Smelling from the outside through the nose.

- Retronasal: Smelling from the mouth while eating.

- Sniffing/slurping boosts smell via air turbulence.

Functions of Smell:

- Warning: Detects threats (ex: rot = disgust, smoke = fear).

- Nutritional: Helps identify food, control intake, catch surprises, support breastfeeding.

- Social: Triggers emotions, helps avoid incest, influences mate choice.

Proust Phenomenon: Smells powerfully trigger memories.

Olfactory Dysfunction and Influencing Factors

different types and their frequencies? causes? what factors improve and worsen functions?

Up to 20% affected by dysfunction:

- Anosmia (5%): complete loss

- Hyposmia (15%): partial loss

- Parosmia: distorted smell

- Phantosmia: smelling odors that aren't present

Causes: nasal disease, neurological disorders, aging, and unknown causes

Often confused with: taste dysfunction

Factors that Improve Function: younger age, female sex, higher education, moderate alcohol use, normal BMI/BP, former smoker

Factors that Worsen Function: older age, active smoking, high BMI, high BP, TBI, Parkinson's, dementia

Trigeminal system

The third chemosensory system alongside smell and taste.
Its receptors are located on trigeminal nerve fibers in the nasal and oral mucosa.

- Responds to chemical stimuli that produce sensations like burning, irritation, tingling, and freshness (ex: menthol, chili, wasabi).

Visual deprivation

Columns in the visual cortex: Focus on left or right eye, with some hybrid cells that process input from both eyes, allowing for 3D vision.

Hubble and Wiesel Experiments

- When a cat's one eye was closed during the critical period, cells dedicated to the closed eye disappeared, forcing the brain to rely exclusively on the open eye

Brain Plasticity in the Blind

Changes in brain structure, function, and performance depend on:

- Age of blindness

- Behavioral relevance of stimuli

In congenital blindness, the visual cortex stays intact despite degeneration of visual pathways

Visual cortex shows intermodal plasticity, often linked to enhanced abilities

Two cross-modal plasticity theories:

- Cortical reorganization – new pathways form

- Unmasking – existing connections are disinhibited and strengthened

Sensory Substitution

one sense (ex: touch) replaces another (ex: vision)

- Functional sense transmits info typically processed by a different modality

- Grants access to perceptual experiences through non-native sensory organs