Lecture 5 Flashcards
(21 cards)
1
Q
How do we sense the world?
A
- Organisms need to sense a wide range of signals in their internal and external environments
- Signals can be radiant energy/chemical or physical forces
- All need to be converted or transduced into signals that can be used by the organism = need to be correctly encoded
- Done via receptors
2
Q
How does the brain contain multiple representations of the body?
A
- Visual system is not everything and is limited
- Only some parts can be seen at all and an odd angle, perception of body does not vanish when we close our eyes
- Afferent inputs from the skin and proprioceptive receptor project to maps of the body surface and body segments respectively in primary somatosensory cortex
3
Q
The skin and somatosensation?
A
- Skin is largest organ
- Primary sense subserving sensation of the body is the somatosensory system
- Comprises all information from the skin = cutaneous sensibility
- 16% of body weight
- Not just receptors - 2 million sweat glands, and 5 million hairs
4
Q
What are the Ascending Pathways - Dorsal Column Pathway for Fine Touch?
A
- Order of fibres as they go into spinal cord tells you where they originate from: fibres climb up to the brain
1st Afferents: - Gracile Fasiculus - fibres entering below the midthoracic level
- Cuneate Fasiculus - upper thorarcic and cervical levels
2nd Neurons: - Nuclei in Gracile and Cuneate nuclei
- Majority of medical lemniscal fibres terminate in the VPL of the thalamus
3rd Neurons: - Thalamocortical projections to primary somatosensory cortex
- Extero receptors = large density of neurones for the body sensory systems that transduce energy whose point of origin is from outside at the interface of the body’s boundaries
5
Q
What is the history of proprioception?
A
- Initially suggested that muscles could signal the brain
- Then Muller suggested that there was no peripheral system needed: just the things that are moving to tell brain where its going: muscle neurons in primary cortex (incorrect as you do need peripheral senses are needed too)
- Proprioception is the sense of position and movement of our limbs, senses of muscle force and effort and sense of balance: the sensation of stimuli that are traceable to actions of the organisms itself
- Active agent in the environment
6
Q
What peripheral receptors drive proprioception?
A
- During limb movement and changes in position, relevant joint tissues will be deformed like skin, muscles, tendons etc.
- The most important are muscle spindles, golgi tendon organs and joint receptors and limited evidence for skin stretch too
7
Q
What happens if muscle is being passively oved or actively moved?
A
- Can stretch muscle fibres by a given force and can measure afferent activity = action potentials generated
- When passively stretched = both have afferent activity but the golgi tendon has weaker/less activity compared to the muscle spindle = vice versa in activity for active contraction = can tell whats happening in body
- Muscle Spindles: respond to changes in length and velocity of muscle
- Golgi tendon: respond to changes in load or force applied muscle
- Helps indicate if you or someone else does that for you
8
Q
How do muscle spindles can consciously affect perception? (kinesthetics illusion)
A
- Vibration applied to tendon of wrist extensor muscle = overloads signal for spindles = reflex contraction = illusory wrist flexion is elicited
- Arm goes out of visual system (cant see)
- Feels like arm is falling away and resetting - can do at any joint = even when arm is not moving
9
Q
Where does cortical processing occur for somatosensation?
A
- BA3a in mammals is the proprioception map = in between M1 (movement and motor) and BA3b (map of skin)
10
Q
What is the body schema?
A
- Spatial perception of one’s body is updated on-line by successive changes in position
- By changing position, we build up a postural model of ourselves, and is recorded on plastic schema
- Activity in cortex brings fresh group of sensations evoked by altered posture into relation with it
- When you drag a cane to a rough floor, you feel the roughness on the end of the cane even when there is not receptors on the umbrella
11
Q
What are features of body schema?
A
- Representation of the positions of body parts in space, which is updated during body movement
- Typically does not enter into awareness although can be forced, but is used for spatial organisation of action
- Body schema is central representation of body’s spatial properties that includes length of limb segments, hierarchical arrangement, config of segments in space and shape of body surface
12
Q
Is the body schema spatially coded?
A
- Integrates tactile information from the body surface with proprioceptive information about config of limbs in space
- Integration means that a stimulus on the body can be localised in external space
- Body schema representation dominate primary representations in normal human behaviour = e.g left hand is better known if compared to right hand in certain area of space
13
Q
How is body schema updated with movement?
A
- Updating may underlie the finding that the visual receptive fields of many parietal neurons follow the hand when the hand moves
- Must be plastic so can adapt for gradual changes in spatial properties of body e.g growing
- With tool use, visual receptive fields of bimodal neurons linked to hand position may move towards the tip of tool
14
Q
Body schema: interpersonal?
A
- Common body scheme is used to represent both one’s own body and bodies of others
- If ppts could better perceive changes in a model’s body posture if they simultaneously moved their own corresponding body part
- Results imply that the observed and self-generated actions were co-represented within a single modular body scheme
- Interpersonal function necessarily implies a supramodal body scheme since info about others is generally visual, while info from one’s own body is generally tactile or proprioceptive
15
Q
How can body schema be disrupted?
A
- Pathologies of sensory input = Deafferentation
- Pathologies of extent = Phantom Limbs
- Pathologies of Updating: Supernumerary Phantom Limbs
16
Q
What was a pathology of sensory input = Deafferentation:
A
- Patient IW lost fine touch and proprioception due to autoimmune response at age 19 that destroyed his ascending system
- Has no body sense or position sense when eyes are closed = managed to regain ability to walk and use limbs again
- Requires constant vision of his body to know where his body parts are and how to move them = primacy of proprioceptive and tactile inputs within the body
- Blind people can achieve accurate sensorimotor control without such an attentional cost = proprioceptive updating of the body scheme is essentially automatic, while visual input may be less so
17
Q
What was a pathology of extent = Phantom Limbs
A
- Map plasticity in the primate somatosensory system
- Traumatic loss of middle finger
- Demonstrates that alterations of input can change map structure in adult animals
- Does not create silent zone, amputated zone driven by adjacent fingers
- Probably was already overlapping system becoming dominant
18
Q
What was a study looking at mouth and phantom hand?
A
- MEG representations of where in the brain we get responses when we touch
- Mouth is next to hand = marker point
- Map the mouth on both sides, and hand on attack side
- Big movement of mouth to where you would expect the other phantom hand to be
- Similar map plasticity in those who record phantom limbs
19
Q
What is the mirror box therapy?
A
- Demonstrates a pure perceptual phantom can move
- Patient concentrates on visual image of lost limb in mirror and to position phantom so it is in the reflection of their hand = strong body schema sense and giving them visual feedback with spatially coinciding thing, then move the real hand
- Visual input overrides body schema and modulates phantom limb pain in a small percentage of ppt
20
Q
What was a pathology of extent = Supernumerary Phantom Limbs?
A
- EP Finnish speaker with no previous psych history and had haemorrhage caused by an aneurysm in left pericallosal artery
- Roughly three weeks after her operation, reported distortions of her body schema which had begun, a third ghost arm
- Prior study also had someone with another arm
- EP would also feel like she would have a third leg, thought she was shoplifting and carrying another bag
- EP could not see her body in the scanner, had earphones for instructions to sync brain activity - let her experience the phantom, and then to move her real right arm (copy of phantom), volitional movement cancels the phantom (after hand moves to a diff position, phantom goes to the position the hand was just at)
- Small but significant activation within a motor area of brain
21
Q
What was the neurophysiology of sustained action?
A
- Evidence that states of motor system can influence perception
- 4 diff locations for monkeys, if you were in a location, monkey would have to move to any other location = rich data set to look at origin of movement wherever of where they go
- Even after executing movement (get goal), still activity within neuron = makes it seem like something is still in space
- Whereas body fires until final goal has been reached (more like an error that decreases when you set goal up)
