Sensation & Perception Quiz 2 (textbook)

The somatosensory system includes

1. Cutaneous senses (responsible for perceptions such as touch + pain that are usually caused by stimulation of the skin)

2. Proprioception (ability to sense the position of the body and limbs)

3. Kinesthesis (ability to sense the movement of the body and limbs)

Cutaneous senses

Everything we feel through our skin (touch, pain, pressure, vibration, tickle, temperature, pleasure)

What are cutaneous senses important for

Grasping objects, protecting against damage to skin, motivating sexual activity

Epidermis

Outer layer of skin, touch dead skin cells

Whats below epidermis?

Dermis

Mechanoreceptors

Receptors that respond to mechanical stimulation such as pressure, stretching, and vibrations

Merkel receptor and mesnier corpuscle

Located close to surface of skin

Small receptive fields

Cutaneous receptive field

Area of skin which when stimulated, influences firing of the neuron

Slowly adapting (SA) fiber

The nerve fibre associated with slowly adapting (merkel) receptor fires continuously, as long as stimulus is on

Rapidly adapting (RA1) fibre

(Meissner) only fires when stimulus is first applied and when it is removed

Merkel receptors (SA1)

Small receptive fields, epidermis

Fires to continuous pressure

Perceives fine details and texture

Perceives shape

Meisner corpuscle (RA1)

Small receptive fields, epidermis

Fires to “on” and “off”

Perceives handgrip control and motion across skin

What kind of receptors do ruffini cylinder have

SA1 (continuous)

What kind of receptors do pacinion cylinder have

RA2/ PC (applied/ removed)

What stimulates ruffini cylinder

Perceiving stretching of the skin

What stimulates pacinion corpuscle

Rapid vibrations and fine texture

Ruffini cylinder (SA2)

Fires to continuous pressure

Perceives stretching

Pacinion corpuscle (RA2/PC)

Fires to on/off

Perceives vibration + fine texture by moving fingers

Where do signals from body conducted from skin to spinal cord receive signals from

Dorsal root (bundle of fibres)

After signals enter spinal cord, nerve fibres transmit them to brain along two pathways

1. Medial lemniscal pathway

2. Spinothalamic pathway

Medial lemniscal pathway

Has large fibres that carry signal related to sensing positions of limbs and perceiving touch

Transmit signals at high speed (reacting to touch)

Spinothalomic pathway

Has smaller fibres that transmit signals related to temperature and pain

What was Ian’s problem

Couldn’t feel touch/ sense position of limbs (lemniscal) but could sense pain and temperature (spinothalomic)

What happens with fibres from both pathways

Cross over to other side of body during journey and synapse in thalamus

(Lateral geniculate nucleus for vision)

(Medial geniculate nucleus for hearing)

Where do most fibres in cutaneous synapse

In ventrolateral nucleus of thalamus

What happens to signals in spinal cord

Cross over to opposite side of body during journey

(L of body, thalamus in R hemisphere, etc)

Pathway from receptors (skin) to somatosensory receiving area of cortex

Touch → dorsal root → spinal cord → spinothalomis tract/ medial lemniscus → thalamus → somatosensory cortex

Fibre carrying signals from receptors enter spinal cord via dorsal root

Signals travel up spinal cord along two pathways

Pathways synapse in thalamus

Sends these signals to somatosensory cortex in parietal lobe

Somatosensory areas in cortex

Two of the areas that receive signals from thalamus → primary somatosensory cortex (S1) in parietal lobe and secondary somatosensory cortex

What are some other somatosensory structures

Insula: sensing light touch

Anterior cingulate cortex (ACC): pain

Somatosensory cortex organized into map that corresponds to

Locations on body

Jacksonian march

Patients seizures progressed on body in an orderly way, with a seizure in one body part followed by seizures in neighbouring parts

Suggested seizures reflected spread of neural activity across maps in the motor area of brain

Homonculus

Shows that adjacent areas of the skin project to adjacent areas in the brain

Some areas on skin are represented by a disproportionately large area on brain

S1 receives inputs from

Ventrolateral nucleus of the thalamus

S2 appearance

Partially hidden behind temporal lobe (smaller)

What parts of body are represented by larger area on the cortex

Parts with the highest tactile acuity

Tactile acuity

Capacity to detect details of stimuli presented to the skin (ex braile)

What can be used to measure tactile acuity

Two point threshold

Grating acuity

Press raised patterns/ letters, determining smallest size identified

Two point threshold

Minimum separation between two points on the skin that when stimulated is perceived as two points

Grating acuity

Measured by pressing a grooved stimulus into the skin and asking the person to indicate the orientation of the grating

Acuity measured by determining narrowest spacing for which orientations can be accurately judged

What creates better acuity

1. Less spacing between merkel receptors

2. Large areas on cortex

3. Small receptive fields

Small receptive fields

Greater cortical separation of touch signals → higher acuity

Large receptive fields

Less precise spatial information (overlap) → lower acuity

What mechanoreceptor is primarily responsible for sensing vibration

Pacinion corpuscle

(Fibres associated respond poorly to slow, constant pushing but respond well to high rates of vibration)

Presence of corpuscle surrounding nerve fiber

Determines which pressure stimuli actually reach the fibre

Consists of series of layers with fluid between each layer

Transmits rapidly repeated pressure (vibration) to nerve fibre

Do not transmit continuous pressure

Causes fibre to receive rapid changes in pressure but not receive continuous pressure

Surface texture

Physical texture of a surface created by peaks/ valleys

Visual perception poorly influenced by illumination (light-dark pattern determined by angle of illumination)

Duplex theory of texture perception

Our perception of texture depends on both spatial cues and temporal cues

Spatial cues

Provided by large surface elements (bumps/ grooves) when skin moves across surface elements and when it is pressed onto the elements

(Shapes, sizes, distributions)

Temporal cues

Occurs when skin moves accros a textured surface like fine sandpaper

Provides info in form of vibrations as a result of movement over the surface

Responsible for our perception of fine texture that cannot be detected unless fingers move across surface

Cortical responses to surface texture

Different textures cause different firing patterns in an individual neuron

Different neurons respond differently to the same texture

Cortical neurons that fired best to coarse textures

Received input from SA1 neurons in skin (Merkel)

Neurons that fired best to fine textures

Received input from PC receptors (Pacinion corpuscles)

Active touch

A person actively explores an object, usually with fingers and hands

Passive touch

Touch stimuli are applied to the skin, as when two points are pushed onto the skin for two pt threshold

Haptic perception

Perception in which 3D objects are explored with the fingers and hands

3 systems used to identify object

1. Sensory system

2. Motor system

3. Cognitive system

Sensory system

Involved in detecting cutaneous sensations such as touch, temperature, and texture, and the movements of your fingers + hands

Motor system

Involved in moving fingers + hands

Cognitive system

Involved in thinking about the info provided by the sensory + motor system

Active vs passive touch

Active touch → you experience the object you are touching

Passive touch → you experience stimulation on the skin

Exploratory procedures (EPs)

People use a number of distinctive (hand) movements to identify an object

Kind of EPs used depends on object qualities judged

Lateral motion, pressure, enclosure, contour following

What would lateral motion/ contour be used to judge

Texture

What would enclosure/ contour be used to judge

Exact shape

Cortical physiology of tactile object perception

Excitatory-center, inhibitory-surround receptive field of a neuron in thalamus

Some neurons in cortex have center surrounding receptive fields

Others respond to more specialized stimulation of the skin

Examples of specialized stimulation of skin that some neurons respond to

Specific orientations, movement across skin in specific direction, grasping ruler vs sphere

2 things cortical neurons are affected by

Properties of an object

Whether perceiver is paying attention

Paying attention

Larger response when paying attention to the tactile stimulus

Size of neural response to some stimulus affected by processes such as attention, thinking and other actions of the perceiver

Active participation not only influences what stimuli stimulate the receptors but also by influencing the processing that occurs once receptors are stimulated

Social touch/ interpersonal touching

You are touched by another person

Disciplines of research on social touch

Social psychology

Cultural anthropology

Cognitive sciences

Neurosciences

Social psychology

How can touch influence a person’s attitude towards other people/ social behaviours, how can touch communicate distinct emotions

Cultural anthropology

Do different cultures, genders, social classes, age populations, have different touch behaviours/ ways of interpreting touch

Cognitive science

How can different tactile sensations be classified, what kinds are unpleasant/ pleasant, perceptual aspects relevant to communicative functions

Neurosciences

Which receptors/ brain areas are responsible for social aspects of touch

CT afferents (C-tactile)

Nerve fibres in hairy skin

Unmyelinated → slower conduction of nerve impulses

Detects light brush strokes, activtion of insula

Caress like skin to skin contact between individuals (social touch stimulation)

Microneurography

Insert metal electrode with very fine tip just under skin to record activity of CT fibres

Social touch hypothesis

CT afferents and their central projections are responsible for social touch

Why is CT different than original system

Different than discriminative functions of touch (sensing details, texture, vibration and objects)

CT system is basis of affective function of touch (sensing pleasure, eliciting positive emotion)

Specialized for slow stroking

Where does the input go when CT afferents reach brain

To insula (involved in positive emotions)

Factors influencing effects of slow stroking

Location and rate of stroking

Knowledge of who is doing stroking

(Perception changes, pleasant/ unpleasant)

Top down (knowledge based) processing affecting of social touch

Pain perception

Warns us of potentially damaging situations (burns, broken bones, etc)

3 types of pain

Inflammatory pain, neuropathic pain, nociceptive pain

Inflammatory pain

Caused by damages to tissue/ inflammation of joins or by tumour cells

Neuropathic pain

Caused by lesions/ other damage to nervous system

Ex of nervous system damage

Carpel tunnel (by repetitive tasks, spinal cord injury or brain damage due to stroke)

Nociceptive pain

Caused by activation of receptors in the skin called nociceptors

Nociceptors

Specialized to respond to tissue damage or potential damage

Different kinds respond to different stimuli (heat, chemical, severe pressure, cold)

Direct pathway model of pain (50s, 60s)

Pain occurs when nociceptor receptors in skin are stimulated and send their signals directly from skin to brain

Ex of ways pain was affected by factors

Soldiers had positive aspect of wounds

Not uncommon for amputees to experience pain in phantom limb (pain originating not in skin, but in brain)

Phantom limb

People who have had a limb amputated continue to experience the limb

Gate control model

Idea that pain signals enter the spinal cord from the body and then are transmitted from spinal cord to brain

Signals from these additional pathways can act to open or close a gate, located in the spinal cord, which determines strength of the signal leaving the spinal cord

What does this gate in spinal cord consist of

Cells in the dorsal horn (+/ -)

Input to gate control system occurs along three pathways

Nociceptors, mechanoreceptors, central control

Nociceptor pathway

Fibers activate circuit of excitatory signals to the transmission cells

Excitatory signals from neurons in dorsal horn ‘open’ gate and increase firing of transmission cells

Inc activity in transmission cells, inc pain

Mechanoreceptor pathway

Fibers carry info about non painful tactile stimulation

Activity in mechanoreceptors (-) reaches neurons in dorsal horn

Inhibiting signals sent to transmission cells ‘close gate’

Decrease firing, decrease pain intensity

Central control pathway

Fibers that contain info related to cognitive functions (expectation, attention, distraction) carry signals down from cortex

Activity carrying down from brain ‘closes’ the gate

Dec transmission cell activity, dec in pain

How does top-down processing influence pain

Pain can be influenced by what a person expects

Placebo

Pill that patients believe contains painkillers but contain no active ingredients

Often get pathological pain relief

Placebo effect

Patient believes substance is an effective therapy

Expects reduction, leads to reduction in pain

Nocebo effect

Negative placebo effect

Negative effect caused by negative expectation

(Thinks off drug, pain inc)

Expectation affects both

Perception and physiological response

How does attention influence pain

Pain sometimes occurs not when injured but when you realize you are injured

Concentrating on different things rather than pain → pain level goes down

Ex: VR