Week 5 - Libet And Neuronal Adequacy Flashcards
Cortigal mapping
(Penfield and jasper)
- somatosneory cortex (sensations of touch that were indistinguishabel from real ines)
Highly intense stimulation evoked
paresthesia-like experiences: electric shocks, tingling, prickling,
numbness, pins-and-needles, etc.
pathological
Gentler stimulation evoked more
natural
experiences: sensations of touch, pressure,
movement, vibration, temperature, etc.
Penfield stimulated many areas besides the somatosensory cortex
• ”Excitable areas”: motor cortex, primary sensory areas; certain areas of the temporal and frontal cortex related to memory and language
- silent areas: association cortex
No stimulation ever porduced
Intellectual behaviour (reaosning)
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.”
Libet
INITIAL RESULTS by libet
- 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
Libet called the…… for neuronal
adequacy
500ms between the start of the train
and conscious experience the threshold
Some typical speeds for neuronal activity:
• 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
Stimulation of non cortical areas
Similar neural activty (evoked potential) as actual stimulus, but not conscious exp.
Backwards masking
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
Subjective referall
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.
Evoked potenital occurs in the
Medial lemniscus (LM) 10-20 ms after sensory stimulation, then occurs in cortex
Backwards referral hypothesis and results
Hypothesis: feel cortical first, skin second.
Results. Feel skin first, cortical second.
TE RMINOLOGY
• CS train:
• S-pulse:
• C-experience:
- S-experience expected:
- S-experience:
• 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
Participants experienced the the S-pulse
as occurring at the time of the S-pulse, before the experience of the CS train, even though the CS train occurred earlier
Did the s pulse and CS train evoke potentials
The S-pulse created an evoked potential, while the CS train did not
Without potential from the cs train. Whats happens
Without an evoked potential, the CS train had no marker for
fetterbacktoevolfotential subjective referral, and was therefore experienced at the time of neuronal adequacy
Libet’s experiments imply that consciousness is an
emergent phenomenon: it emerges from neural
activity when that activity achieves neuronal adequacy (why?)
Libet also claimed that backwards referral was a serious threat to
materialism
: “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.”
John Eccles
Responces to libet
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
