PSY260 Lecture 11: Plasticity in Damage/Injury

Terminology Surrounding Brain Damage

• “Damage“ is a relative term, and what we usually mean is change

  • Our brains are constantly changing tin response to their environments

    • Sometimes good: learning, growing adapting

    • Sometimes bad: damage, injury, deterioration

• Some wear-and-tear to our brains is inevitable

Brain Damage: Causes

1. Congenital/developmental

   1. Genetic disorders; prenatal infections, exposure to toxins in utero, nutritional deficits during development

2. Trauma

   1. Birth trauma, falls/accidents, concussions, blast/penetration, injuries

3. Vascular

   1. Stroke, high/low blood pressure

4. Metabolic

   1. Nutrition deficits, includes drug abuse

5. Infections

6. Tumours

7. Inflammation

   1. Even when activated by the body as a defense

Brain Damage: Distribution

1. Focal

2. Diffuse

3. Mixed

Focal Brain Damage

• Damage contained to a specific area or region

  • Ex. stroke, tumour, focal ifections

• Can be easier to find relationships between damage and symptoms

  • Because the damage is localized

• Often better prognosis because other undamaged regions can take over functions

  • Compensation with plasticity

Diffuse Brain Damage

• Widespread across multiple brain regions

  • Ex. traumatic brain injury (shakes whole brain), hypoxia, infections, neurodegenerative diseases

• More complex symptom profiles → multiple systems affected

• Harder to target rehabilitation

  • Located in multiple places

Mixed Brain Damage

• A combination of focal and diffuse damage

  • Can originate in one place, then spread outwards

Brain Damage: Timing (During Gestation)

• 1st trimester:

  • Damage tends to affect development of major structures

  • Disrupts foundational development, tends to be most severe

  • BUT maximum potential for alternative development pathways due to extreme plasticity

• 2nd trimester:

  • Damage tends to affect cortical organization

  • Recovery depends a lot on extent and location of damage

• 3rd trimester:

  • Damage tends to be more focal

    • More areas are developed

  • Still significant plasticity, but more constrained than earlier periods

Brain Damage Timing: Infancy

• Very high plasticity, especially in sensorimotor areas

• Language can still lateralize to the right hemisphere if the left is damaged at this stage

  • Can still compensate

Brain Damage Timing: Childhood

• Early (2-7):

  • Strong plasticity

  • Recovery potential remains very good

• Late (7-12):

  • Plasticity starts to decline

  • Recovery more dependent on targeted interventions

  • Greater need for good treatment

Brain Damage Timing: Adolescence

• Plasticity slows

• Frontal regions still highly modifiable

  • Keep developing until mid-20s

  • Frontal and PFC

Brain Damage Timing: Adulthood

• Brain development completed at mid-20s

• Gradual decline in natural plasticity

• Recovery requires more active intervention and practice

• Increasing importance of cognitive reserve

  • Building up alternative pathways BEFORE brain damage to help with compensation if there ever is any

Brain Damage Timing: Older adulthood

• Higher vulnerability to damage

• Plasticity still present, but even more reduced

  • Recovery often takes longer

• Recovery focused on functional compensation

  • Trying to use what’s still working better

  • Instead of trying to recover what is damaged

• Cognitive reserve very important for outcomes

  • Building up alternative pathways BEFORE brain damage to help with compensation if there ever is any

Brain Reorganization

• Equipotentiality

• Vicariation

Equipotentiality

• When an area in one hemisphere of the brain is damaged, the corresponding area in the other hemisphere can take over its function

  • Ex. language development in infancy can switch to right if left is damaged

Vicariation

• Reorganization of other (adjacent) brain areas take over function of a damaged area

  • Same hemisphere → nearby brain regions

Structural Reorganization

• Angiogenesis

• Spinal neuroplasticity

Angiogenesis

• Formation of new blood vessels

  • Especially following vascular damage

  • ↑ O2 carrying ability

  • Can increase with aerobic exercise

Spinal neuroplasticity

• Growth of new synaptic spines

  • Changing network

  • Rare to see new neurons (neurogenesis) outside of gestation-infancy

Functional Reorganization

• Ipsilesional reorganization

• Contralateral reorganization

  • Crowding effect

Ipsilesional Reorganization

• Same side as lesion → like vicariation

  • Ex. right premotor cortex taking over right primary motor functions following rM1 damage

• More likely following mild/moderate damage, focal damage

Contralateral Reorganization

• Opposite side of lesion → like equipotentiality

  • Ex. right hemisphere taking over language processing following left hemisphere damage in utero/infancy

• Crowding effect

• More likely following moderate/extensive damage, diffuse damage

Crowding effect

• Deficits in the functions typically supported by the repurposed hemisphere

  • Ex. right hemisphere normal function may suffer because it takes on additional responsibility of lef hemisphere functions

Adaptive Neuroplasticity

• Refers to any structural or functional change that is beneficial

  • Changes that improve function

  • General examples

    • Learning new skills

    • LTP

    • Strengthening/increasing efficiency of useful circuits

    • Recovery of function following injury

Maladaptive Neuroplasticity

• Refers to structural or functional changes that are harmful

  • Changes that worsen function/cause problems

  • General examples

    • Phantom limb pain

    • Other forms of chronic pain

    • Trauma flashbacks

Critical Periods

• Both timing of damage AND treatment factor into effectiveness

• Trying to force rehabilitation too early → can have adverse effects

  • First 24-48 hours after stroke → not recommended

• Most rapid recovery occurs first 3-6 months after damage/injury

  • This is where the greatest gains are made

  • Not to say that there can’t be recovery after

• Recovery can continue for months or years after injury

Promoting Plasticity

• Task-specific training/practice

• Environmental enrichment

• Non-invasive brain stimulation

• Medications

Promoting Plasticity: Task-specific training/practice

• Do the thing you’re struggling with

  • Try to directly restrengthen damaged pathway

• May also inhibit use of compensatory strategies

  • Constraint-Induced Movement Therapy (CIMT)

    • Ex. stroke recovery → restrain working arm to force use of damaged arm

    • Can be frustrating

Promoting Plasticity: Environmental enrichment

• Sensory stimulation, social interaction, cognitive challenges

• Use of tools and other stuff to challenge brain

Promoting Plasticity: Non-invasive brain stimulation

• TMS, tDCS

  • Use to manipulate brain activity

  • Relatively new

• Increase plasticity in affected areas

• Inhibit compensatory areas

  • Like CIMT for brain

Promoting Plasticity: Medications

• Certain stimulants, SSRIs, cholinesterase inhibitors

  • Relatively new

• Psychedelics: ayahuasca, DMT, psilocybin, and LSD

  • Can increase neurotransmitters (serotonin) which promote plasticity

“AL“ Phantom Limb Pain: Damage

• 35 year old man whose right leg was amputated after a car crash

• Activity in the part of his primary somatosensory cortex (S1) that corresponded to the missing leg → experienced as phantom pain

  • Could light up as part of other pathways

• Said it felt like his foot was flexed and he couldn’t unflex it

“AL“ Phantom Limb Pain: Symptoms

• Touching thigh above amputation point elicited sensations in phantom toes

• Researchers had a volunteer (V) place her right leg near the phantom lef

  • Seeing V’s leg touched → could feel sensation in his phantom leg

  • When V pointed her foot → felt relief in his phantom leg, as if it was unflexed

  • Also felt relief when V’s foot was massaged

• Mirror Visual Therapy (MVT) offered temporary relief

“AL“ Phantom Limb Pain: Treatment

• Pain medications were NOT effective

• Mirror Visual Therapy (MVT) → temporary relief

• Psilocybin → temporary relief

  • Helps ↑ plasticity → S1 area of missing limb can remap over time

• MVT + psilocybin → lasting relief from the pain

• AL felt less pain with time

“AL“ Phantom Limb Pain: Conclusions

• ~95% of people who undergo amputations experience phantom pain or itching

  • Very common, almost expected

• Effectiveness of MVT helps us understand the role of mirror neurons

  • Neurons that respond to watching someone else undergo a sensation

  • Involved in empathy

• Effectiveness of psilocybin helps us understand the role of serotonin in promoting neuroplasticity

  • May make brain more receptive to MVT

  • When used in combination with MVT, can lead to lasting pain relief

“Anonymous Frenchman“ Hydrocephalus: Symptoms

• 44 year old male went to hospital with mild weakness in his left leg

  • Lived a normal life, worked, had a family

  • IQ was 75ish (below average but normal still)

• Diagnosed with hydrocephalus (extra fluid in brain) as an infant

• Treated with a stent to drain fluid,

  • Was removed at age 14

• No other physical or cognitive symptoms reported

“Anonymous Frenchman“ Hydrocephalus: Damage

• Significantly enlarged ventricles

  • HUGE and filled with CSF, took up ~90% of the space within his skull

• Remaining brain matter compressed to the areas right around his skull

  • SEVERE squishing

“Anonymous Frenchman“ Hydrocephalus: Conclusions

• Unclear whether his neurons had died or been squished over time

  • Likely a combination

• If damage occurs gradually enough, the brain has a remarkable ability to find ways to continue functioning normally

  • Speed matters → faster will cause a lot more damage

  • His brain had likely been having to constantly rewire and form new compensatory networks as more fluid collected in the 30 years after his stent was removed

  • Constant compensatory plasticity

• Amount of damage doesn’t necessarily correlate with severity of symptoms

Jason Padget (“Math Guy“) Acquired Savant Syndrome: Damage

• Suffered blow to the back of his head while getting mugged

  • Suffered a concussion

• Damage was primarily in temporal and parietal lobes

• Mostly in the left hemisphere

• Ended up being beneficial

Jason Padget (“Math Guy“) Acquired Savant Syndrome: Aftermath

• Developed OCD and PTSD after injury

• Also began to see the world through the lens of advanced math

  • Began to perceive geometric patterns that mapped onto patterns in math and physics

Jason Padget (“Math Guy“) Acquired Savant Syndrome: Considerations

• Reliance on self-report

  • Told his own story via social media, could be exaggerated

• Intuitive understanding of geometric patterns sometimes overstated as a general genius across all math

  • May be more accurate to think of it as a perceptual phenomenon, more like synesthesia (pairing sensory types)

Math Guy: Similar Cases

• Orlando Serrell:

  • Hit with a baseball → developed calendar calculating abilities

• Anthony Cicoria:

  • Struck by lightning → developed sudden musical abilities

• Tommy McHugh:

  • Stroke → artistic abilities

• All seem to gain less verbal abilities (mathematical/artistic)

  • Damage is often on left, new abilities often associated with right hemisphere

Jason Padget (“Math Guy“) Acquired Savant Syndrome: Conclusions

• Only 30-40 cases diagnosed with acquired savant syndrome

• Often resulting from left hemispheric damage

• Often involved acquisition of new abilities related to math, music and art

  • Functions typically associated with right hemisphere

• Theory of Paradoxical Functional Facilitation

  • Damage may release right hemisphere areas from interference, uncovering latent abilities

  • TMS that inhibits left hemisphere → can produce similar improvements in perception/artistic ability

    • Effects are much more transient/temporary with TMS

    • tDCS is not powerful enough to last

“Jan“ Broca’s Aphasia: Overview

• Stroke at age 31 in the left frontal cortex

• Affected language production (Broca’s aphasia)

  • Could still understand and knew what he wanted to say

  • Couldn’t produce the words to say it

• Affected strength and coordination in right side of the body

  • Contralateral

  • Struggle with planning

• With lots of rehab, gradually gained back ability to walk and talk