Week 5 - Libet And Neuronal Adequacy

Question 1

Cortigal mapping

Answer 1

(Penfield and jasper)

- somatosneory cortex (sensations of touch that were indistinguishabel from real ines)

Question 2

Highly intense stimulation evoked

Answer 2

paresthesia-like experiences: electric shocks, tingling, prickling,
numbness, pins-and-needles, etc.
pathological

Question 3

Gentler stimulation evoked more

Answer 3

natural
experiences: sensations of touch, pressure,
movement, vibration, temperature, etc.

Question 4

Penfield stimulated many areas besides the somatosensory cortex

Answer 4

• ”Excitable areas”: motor cortex, primary sensory areas; certain areas of the temporal and frontal cortex related to memory and language

• silent areas: association cortex

Question 5

No stimulation ever porduced

Answer 5

Intellectual behaviour (reaosning)

Question 6

To study the causal relationship between specific neural actions and subjective experience requires an ability to manipulate neural function in a controlled manner; direct intracranial electrical
stimulation in the conscious human subject is one of the very few approaches available for such purposes.”

Answer 6

Libet

Question 7

INITIAL RESULTS by libet

Answer 7

• Intensity (I): peak electric current applied to the tissue
• Train Duration (TD): the duration of time for which stimulation (60 pps) was applied
• discovered lamina 1: min intensity to elicit conscious exp.
  (Required TD was 500ms for conscious exp)
• I and TD inversed

Question 8

Libet called the…… for neuronal

adequacy

Answer 8

500ms between the start of the train

and conscious experience the threshold

Question 9

Some typical speeds for neuronal activity:

Answer 9

• Time for auditory stimuli to transmit from the cochlea
to the brain: 8-10ms
• Time for visual stimuli to transmit from the retina to the
brain: 20-40ms
• Reaction time to visual stimuli: 150-200ms
• Visual recognition of stimuli: 3-400ms

Question 10

Stimulation of non cortical areas

Answer 10

Similar neural activty (evoked potential) as actual stimulus, but not conscious exp.

Question 11

Backwards masking

Answer 11

Cortical stimulation masks the conscious experience of prior sensory stimulation up to 500ms later
- simce they require same neuronal resources, if cortigal interferance occurs up to 500ms after the touch, skin stimuli wont be consciously. percepved

Question 12

Subjective referall

Answer 12

The explaination to how we are living 500mx behind reality or event in the world. Our conscious exprrinces are subjectivly refered backwards in time by our brains to fix this “gap” and so we feel like we percieved it when it occured.

Question 13

Evoked potenital occurs in the

Answer 13

Medial lemniscus (LM) 10-20 ms after sensory stimulation, then occurs in cortex

Question 14

Backwards referral hypothesis and results

Answer 14

Hypothesis: feel cortical first, skin second.

Results. Feel skin first, cortical second.

Question 15

TE RMINOLOGY
• CS train:
• S-pulse:
• C-experience:

• S-experience expected:
• S-experience:

Answer 15

• CS train: stimulus train applied to the somatosensory cortex
• S-pulse: pulse applied to the skin at liminal I
• C-experience: the conscious experience of the C-train
• Required the C-train to be applied for up to 500ms
• S-experience expected: the expected time at which participants would experience the S-pulse, given the threshold
for neuronal adequacy
• S-experience: the actual time at which participants participants reported experiencing the S-pulse

Question 16

Participants experienced the the S-pulse

Answer 16

as occurring at the time of the S-pulse, before the experience of the CS train, even though the CS train occurred earlier

Question 17

Did the s pulse and CS train evoke potentials

Answer 17

The S-pulse created an evoked potential, while the CS train did not

Question 18

Without potential from the cs train. Whats happens

Answer 18

Without an evoked potential, the CS train had no marker for

fetterbacktoevolfotential subjective referral, and was therefore experienced at the time of neuronal adequacy

Question 19

Libet’s experiments imply that consciousness is an

Answer 19

emergent phenomenon: it emerges from neural

activity when that activity achieves neuronal adequacy (why?)

Question 20

Libet also claimed that backwards referral was a serious threat to

Answer 20

materialism

Question 21

: “This antedating procedure does not seem to be explicable by any neurophysiological process. Presumably it is a strategy that has been learnt by the self-conscious mind.”

Answer 21

John Eccles

Question 22

Responces to libet

Answer 22

Blackmore: disputes the dualist implication: we subjectively refer events in space (we perceive them as “out there” in the world,
rather than “in here” in the brain) so why not time as well?

Churchland:

• reliance on after trial reports and memory
• 500ms backwards mask inly worked for one participant, sometimes 200ms was common
• s-pulse may not reuire NE in the same way C-trians do. If normal delay was 300ms bw skin stim and conscious percpetion, then the nirmal result would be S-experience first, C-experience second.
• didnt follow ockhams razor