Plato’s Allegory of the Cave

Plato’s Allegory of the Cave – Alex Gendler


If You Don’t Know You Are Held Captive, Does It Matter?
June 10, 2015
Marcelo Gleiser

the classic movie The Matrix. As a counterpoint, they also read Plato’s “Allegory of the Cave” from Book VII of his dialogue The Republic. Both can be seen as explorations of the value of knowledge and freedom.

If you were a chained slave or a human in a cocoon, would you like to know? Is “ignorance is bliss” a viable life?


Consciousness is a mathematical pattern
Max Tegmark at TEDxCambridge 2014



Non-conscious perception of emotional signals

Neural bases of the non-conscious perception of emotional signals
Marco Tamietto & Beatrice de Gelder
Nature Reviews Neuroscience 11, 697-709 (October 2010)

Many emotional stimuli are processed without being consciously perceived.
Recent evidence indicates that subcortical structures have a substantial role in this processing.
These structures are part of a phylogenetically ancient pathway that has specific functional properties and that interacts with cortical processes.
There is now increasing evidence that non-consciously perceived emotional stimuli induce distinct neurophysiological changes and influence behaviour towards the consciously perceived world.
Understanding the neural bases of the non-conscious perception of emotional signals will clarify the phylogenetic continuity of emotion systems across species and the integration of cortical and subcortical activity in the human brain.

Jazz pianist recovered from AIDS-related dementia

Fred Hersch Floats On, With A Dynamic Trio In Tow
July 19, 2014

The last time Fred Hersch was featured on Weekend Edition Saturday, the headline read, “Back On Stage By No Small Miracle.” It was 2009, and scarcely a year earlier, the jazz pianist had suffered AIDS-related dementia and fallen into a coma for several months.
Since recovering, Hersch has come roaring back to music, releasing a string of live albums to critical success.

A new studio recording by Hersch’s trio came out earlier this month; it’s called Floating.
This week, a review in The New York Times said that while Hersch has been putting out great trio albums for 30 years, “He hasn’t made one better than this.”

How the EEG correlates with consciousness: unknown (2011)

Decapitation in Rats: Latency to Unconsciousness and the ‘Wave of Death’
Clementina M. van. Rijn mail, et al.
PLOS ONE. January 27, 2011

In awake rats it lasts takes about 17 seconds before the power of the EEG is iso-electric.
Since it is not known how the power of the EEG correlates with the level of consciousness, in drug free subjects, iso-electricity forms a solid base to regard the animal as completely unconscious.
However, the question arises whether the degree of consciousness at an earlier time is already so low that perception of pain and distress is already totally eliminated.

the power in the cognitive band (13–100 Hz) of the sleep state is still 78%, (SEM 4.4%) of that during waking.
Since sleep is not deeply unconscious, it seems save to take a lower value, thus to assume that the animals are unconscious at a power decrease of the cognitive band of 50%.
This point is reached in 3.7 seconds.

The EEG of an anesthetized subject is very different from that of an unmedicated state.
Therefore it is quite surprising that the post-decapitation EEG, and its power, of the anesthetized group are almost the same as that of the awake group.
One interpretation is that the resulting power of the EEG in the awake animals is not well indicative of consciousness and distress, since the same activity is present in the EEG of non-conscious anesthetized animals.
On the other hand, the resemblance of the power of the post decapitation EEG in both groups might also imply that the animal’s consciousness is briefly enhanced immediately after the neck cut.
The interpretation might be that the cut is such a powerful arousal stimulus, that even anesthetized animals regain consciousness.

A relatively long time after cutting the neck, when iso-electricity is already present in the EEG for a considerable time, a large amplitude positive-negative-positive wave follows at approximately 50 seconds after decapitation of rats of the awake group.
In the anesthetized rats this wave is also present but comes later, at about 80 seconds after the neck cut.

it seems that it takes nearly one minute for neurons to loose their membrane potentials.

this paper is cited by:
Death rattle of a decapitated brain
09 February 2011
New Scientist, issue 2799, pp: 8-9

NewScientist also cites:
Surges of electroencephalogram activity at the time of death: a case series.
J Palliat Med. 2009 Dec;12(12):1095-100.
increase in electrical activity occurred when there was no discernible blood pressure

Successful resuscitation after prolonged periods of cardiac arrest: A new field in cardiac surgery
The Journal of Thoracic and Cardiovascular Surgery. 139(5):1325–1332.e2, May 2010

Reply to Chawla and Seneff: Near-death electrical brain activity in humans and animals requires additional studies
Jimo Borjigin, et al.
PNAS. October 29, 2013, vol. 110 no. 44
the details of the algorithm used to generate Bispectral Index (BIS) values are proprietary, and therefore it is currently impossible to make a direct comparison of our study with those using the BIS monitor.

Absolute measures for loss-of-consciousness: don’t exist (2007)

Loss of Cortical Function in Mice After Decapitation, Cervical Dislocation, Potassium Chloride Injection, and CO2 Inhalation
Comparative Medicine. December 2007. 57(6): 570–573

surrogate measures of cerebral cortical function

Two such measures that have been used widely are the electroencephalogram (EEG),13,19 which provides a gross measure of overall neuronal activity, and evoked potentials, which measure focal cortical responses to a specifi c stimulus such as a flash of light (for example, visual evoked potentials; VEPs).6
An absolute absence of EEG activity or VEP indicates complete unconsciousness to the point of brain death.
The intermediate degree of alteration in EEG or VEP amplitude that correlates with loss-of-consciousness is unknown.

The 2000 Report of the AVMA Panel on Euthanasia2 (2000 Panel) changed the recommendation for decapitation from the 1993 Panel1 to clearly indicate that decapitation produces a rapid loss of consciousness.
The recommendations of the 2000 Panel dismiss the erroneous conclusion that the EEG activity that occurred for 13 to 14 s after decapitation of rats13 was indicative of consciousness or pain.

The acceptance of decapitation as a method of euthanasia that does not require scientific justification establishes it as an appropriate method against which to compare other methods that may be controversial or require scientific justification, such as cervical dislocation and CO2 administration.11,16,17,20

Data collected during the first 30 s after the euthanasia were quantitatively analyzed based on our assumption that an animal is unconscious 30 s after decapitation.
Oxygen tension in the decapitated rat brain falls to levels associated with unconsciousness within 3 seconds[5]; therefore, a similar phenomenon is likely to occur in a decapitated mouse brain within 30 s.
Such assumptions are necessary because absolute measures for loss-of-consciousness do not exist.
If this assumption is accepted, then data gathered more than 30 s after decapitation are artifacts of an unconscious state.


Paradox: fragmented memories, strong sense of self

Our Brain, The Trickster
May 28, 2014
by Marcelo Gleiser

It’s an interesting paradox that, even though our memory of past events is so faulty and fragmented, our sense of self remains strong day in and day out.

there’s a lot of debate among cognitive scientists about the so-called “theater of the self” — the notion that a movie plays inside our heads continually.
[Cartesian theater]

Failure of Inhibitory Control on an Ambiguous Distractor

bidirectional interactions between the LPFC and MT+.

Greater disruption due to failure of inhibitory control on an ambiguous distractor.
Science 314:1786-1788. (15 December 2006)
Tsushima Y, Sasaki Y, Watanabe T

Second, the results may reveal important bidirectional interactions between a cognitive controlling system and the visual system.
The LPFC, which has been suggested to provide inhibitory control on task-irrelevant signals (22–26), may have a higher detection threshold for incoming signals than the visual cortex.
Task-irrelevant signals around the threshold level may be sufficiently strong to be processed in the visual system but not strong enough for the LPFC to notice and, therefore, to provide effective inhibitory control on the signals (Fig. 4A).
In this case, such signals may remain uninhibited, take more resources for a task-irrelevant distractor, leave fewer resources for a given task (32, 33), and disrupt task performance more than suprathreshold signals.
On the other hand, suprathreshold coherent motion may be noticed, may be given successful inhibitory control by the LPFC, and may leave more resources for a task (Fig. 4B) (22–26).
This mechanism may underlie the present paradoxical finding that subthreshold task-irrelevant stimuli activate the visual area strongly and disrupt task performance more than some suprathreshold stimuli.
It could also be one of the reasons why subthreshold stimuli often lead to relatively robust effects (2, 11, 14).

MT+: human middle temporal visual area
LPFC: lateral prefrontal cortex

cited by: