Week 11 - Sensory Deprivation

Question 1

Sensory deprivation is sometims called

Answer 1

perceptual isolation

Question 2

Sensory Deprivation in Experiments and real life

Answer 2

In experiments; a deliberate reduction or removal of sensory stimuli from one or more modality for scientific study

In read life; deliberate or unintended reduction or removal in sensory stimuli from one or more modality for a number of reasons

eg. deliberate methods; therapy, relaxation, curiosity, amputation, interrogation/torture, punishment
eg. unintended; tissue/neural damage, other clinical conditions

Question 3

deprivation tanks

Answer 3

• developed in the 40’s by John Lily for quasi-experimental purposes
• is no used for relaxation and alternative medicine
• has no light, no sound, no gravity
• claims to relieve stress, anxiety, pain and fatirue
• evidence; reduces stress but not much else (and even then, studies havesmall samples and prone to bias )

May serve as evienece for transient sensory loss having benefits

Lily wanted to explain the effect of consciousness in snesory deprivation but was mocked for later LSD use and crap science pre much

Question 4

Anechoic Chambers

Answer 4

• serve as evidence for transient sensory deprivation being not good (unlike deprivation tanks which at minimum are relaxing for some)

In these chambers, there is very low background noise and sensory sensitisation occurs rapidly

• ost people can’t last in the room for more than a few minutes as their heartbeat becomes very loud etc

For some however, this is very relaxing and they stay in for an hour or more - this is true for clinical populations who have sensory difficulties

In the Microsoft HQ anechoic chamber the background noise is -20.35 dB - is the worlds quietest room

Question 5

Beatriz and Falmini 2021

Answer 5

spend 500 days underground. She emerged 14.4.23
- had no human contact, diminished light, diminished sound, diminished olfactory/gustatory cues, diminished somatosensory stimulation

She said the experience was excellent, and unbeatable
when she came out she had lost her sense of balance and had to be held

she also experiences auditory hallucinations - as the brain made up the missing noise

Question 6

Role of volition in enjoying sensory deprivation

Answer 6

If you choose to do something your experience will differ

Question 7

White Room Torture

Answer 7

shows the importance of volition
- these are completely white rooms that are sound proofed. All surfaces are smooth, meals are intentionally bland in appearance, taste, smell and texture

Causes disorientation, disequilibrium, confusion, hallucination etc

Question 8

Where does the white room method come from?

Answer 8

Ganzfeld effect (Metzer 1930)
= where the whole field perception is kept uniformly featureless

This experience consistently triggers visual hallucinations and altered EEG activity in the occipital lobe (visual cortex)

Onset within minutes, typical hallucinations include patterns, shapes, flashes of light/colour but can be more complex (figures, objects, scenes)

Has then been co-opted as a method for purposefully disorienting and confusing someone

Multi-modal Ganzfeld; use of ganzfeld gogles and ganzfeld headphones

Ganzfeld methods and white room torture believed to be in use in at least 4 countries

Ganzfeld effect has actually been known since ancient times (since pythagorus)
- greek scholars went to caves epeirence visions
- miners report hallucinations if trapped in dark mines
- artic explorer experience hallucinations during whiteout conditions
- only seriously researched from 1930s then led to many strange inventions and para-scientific lines of research

eg. sensory deprivation to develop psychic 6th sense also machines attempting to recreate the strobing flash light hallucinations that were though to represent an altered state of consciousness (this is actually why strobe lights in nightclubs started)

Question 9

charles bonnet Syndrome

Answer 9

• aka visual release hallucinations
• first described in 1760 - where vivid, recurrent visual hallucinations occur after going blind (partially or completely)
• most common in elderly (as is vision loss) but an occur at any stage
• simple shapes/patterns/colours > extremely complex scenes
• common reports ‘ lilliputian’ (aka mini objects or people, or cartoon faces, creatures, buildings, vehicles)
• present in 10 -40% of cases of vision loss

was uncovered as charges bonnet’s grandfather went blind then had hallucinations

Prevalence for this is increasing likely due to improves culture

Question 10

Hearing loss-induced tiniitus

Answer 10

aka auditory hallucinations; typically ringing/buzzing or high-pitched hissing

Approx 90% of people with tinnitus have hearing loss, and the phantom percept usually mimics what was lost

eg. hearing loss at high frequency results in high pitched phantom sounds

Tiniitus doesn’t have to come from hearing loss (there are other causes) this is just one example

Question 11

Phantom Limb Pain

Answer 11

First documented in the 16th centruy
- today, it’s acknowledged that virtually all amputees experience phantom limb sensations; pain, itch, tickle, tough
this can be mild or extremely debilitating

can occur from differentiation - ie sci
or from the removal or a limb

Question 12

What forms of involuntary hallucinations from sensory loss aren’t well documented

Answer 12

Anosmia and Ageusia

• there is little evidence to link anosmia and phantosmia or agueia with phantogeusia

Question 13

Homeostatic Plasticity as a cause for phantom percepts

Answer 13

Argues that neurons need to maintain firing at a preferential level
- neurons are tuned in development t. fire at a given baseline frequency and seek to maintain this

This is because;
- too little activity makes neurons uneconomical
- too much activity is dangerous (cytotoxic and seizure risk etc)

Question 14

Homeostatic Plasticity and Synaptic Scaling

Answer 14

When sensory loss occurs, the input and therefore firing rate of a given neuron decreases

Homeostatic plasticity is the process of restoring neural activity to a preferred level by changing strength of their synapses

• activity deprivation triggers synaptic ‘upscaling’ to restore output
• activity enhancement triggers synaptic downslcaing to restore output

Question 15

Synaptic Upscaling

Answer 15

Occurs when firing rate is chronically lowered experimentally (in vivo or ex vivo) or through natural causes
- to store firing rates back to normal the synapse increases its strength to provide more input/depolarisation and encourage firing
Is achieved with a greater number of presynaptic NT being released or a greater number of receptors in the synapse

Question 16

Synaptic Downscaling

Answer 16

• where firing rate is chronically elevated (experimentally or through natural means like seizure (status epilepticus)
• so downscales firing by tweaking the synapse strength
  This infolves a reduction in NT release, and fewer receptors in the membrane

Question 17

Linking synaptic scaling and sensory deprivation

Answer 17

• loss of sensory input should trigger homeostatic synaptic upscaling
  at least in the visual, auditory and somatosensory pathways (but likely in more )

Question 18

Rodent model evidence for synaptic scaling

Answer 18

in visual pathway;
- after eye suturing or enucleation there is upscaling of neurons in the visual cortex

In the auditory pathway;
- after inner ear damage there is upscaling of synapses in the auditory cortex, colliculus and thalamus

In somatosensory pathway;
- whisker removal leads to upscaling of synapses in the somatosensory cortex (aka the barrel cortex)

Question 19

TNF and Honeostatic Synaptic Plasticity

Answer 19

Tumor Necrosis Factor (TNF)
- is a cytokine
- potent regulator of synapse strength and plasticity
- released from glial cells (astrocytes and/or microglia) following loss of input to nearby neurons

Astrocytes release TNF onto a synapse
Microglia release TNF more globally

When Firing in a pathway reduces, TNF is released to drive synaptic upscaling processes

Question 20

Evidence of TNS in Synaptic Scaling in Humans

Answer 20

In human studies, many papers show upregulated TNF levels are associated with hallucinations following different forms of sensory deafferentation (measured spinal TNF and correlated to hallucinations. Has also explored people with certain polymorphisms that increase TNF)

Somatosensation - TNF levels elevated in limb amputees, correlates with phantom limb pain and TNF inhibitor reduce phantom pain symptoms

Audition; Tinnnitus is associated with elevated TNF levels. RElaxation training that improves tinnitus symptoms also reduces TNF levels

Question 21

Charles Bonnet and TNF

Answer 21

no studies have explored TNF and Charles Bonnet Syndrome

But many studies showing increased TNF levels in conditions associated with visual hallucinations and antipsychotics that reduce hallucination frequency/severity also reduce TNF levels but this link is still speculative

Question 22

How can homeostatic changes account for additional phenomenon seen after the loss of a sensory modality

Answer 22

Cross-modal plasticity ; lose one modality, scale up the capacity in another (eg. Richard Emerson, is deaf but good at tasting and smelling)

• eg. improved hearing in blind people ( a lower absolute and relative threshold and better sound localisation)
• involves repurposeing the unused cortex to improve function in remaining modalties - may be done through synaptic scaling within the modality orrr cross-modal repurposing of the cortex

Question 23

Disinhibtion hypothesis in sensory deprivation cases

Answer 23

Suggests we have projections between sense modalities in the brain but they re under heavy inhibition
- anatomical studies have identified projections between sensory cortices including
V1 –> S1
V1 –> A1
A1 –> S1

Some of these projections are excitatory and some are inhibitory

There is some evidence that cross-modal plasticity may involve these projections

Question 24

Evidence for Cross-modal and disinhibition hyptohesis

Answer 24

• Hashimoto et al., 2023
  In mice, monocular deprivation leads to compensatory upregulation of somatosensory function (lower threshold for discriminating whisker stimulation)
• involves activation of V1 by whisker stimulation

This is likely due to microglial cells puning local inhibitory synpases to unmask cross-modal plasticity

Question 25

TNF mediated synaptic upscaling may..

Answer 25

contribute to sensory deprivation-induced pahtom percepts/hallucinations

it’s speculative but TNF may also contribute to snesory deprivation induced cross-modal plasticity

But - it may be only one of the many mechanisms that underlie such experiences and TNF can cause neurological disease (so it’s not like the more the better)

Question 26

Sensory deprivation and Dementia

Answer 26

8-9% of dementia cases can be accounted for by hearing loss worldwide
visual impairment is believed to account for 1.8% of cases
47% of cases is believed to also present with chronic pain (real or phantom) and is believed to accelerate pathogenesis even if it doesn’t necessarily cause it

Question 27

TNF is hugely elevated in the brains of people with

Answer 27

Alzheimers

It’s believed to be at least partly responsible for learning and memory deficits (acting on cells/synapses in the hippocampus and other memory regions - like the limbic system0
- is believed to contribute to cell death

Question 28

A potential confound in dementia research

Answer 28

• dementia is multi-factorial. So sensory depreivation could drive dementa through many pathways
  1. Atrophy of unused brain cells/circuits
  2. neuroinflammation via TNF-dependant homesoatic plasticity
  3. Social isolation - a huge contributor to dementia progression

Question 29

Good news on sensory loss, dementia etc

Answer 29

hearing loss can increase the risk of dementai but the use of hearing aids can aid or reverse that risk
the same with visual deficits