NEURO - Lecture 6 - T3

Effects of rehabilitative training on cortical motor maps and function after cortical infarct - monkey outcomes

* using taubs technique -**retraining of affected hand ENLARGED the representation in cortex abov norm and at the expense of the proximal arm

Ramachandran studied patients who had lost an arm (e.g. VQ) - what did he see in topography changes in VQ

- - perceptual consequences of map reorganization are shown by studies of phantom limb sensations in humans: - some had consistent phantom sensations evoked by stimulation to the face and upper arm stump***ie stim the face feel phantom**

who showed that neurogenesis occured and when

- In late 1990′s, Elizabeth Gould showed clear evidence of neurogenesis in rodent and primate (including humans) in the hippocampus

What happens if input to part of the map in cortex is removed? (e.g. after amputation)

- Somatosensory cortex reorganizes after amputation: representation of digit 3 in SS cortex is taken over by adjacent cortical areas ***immediately after amputation cortex = silent in the area of the amputated finger topographically, by 2 mos post surgery cells in that area = responsive to stim of adjacent fingers

compare the amputated monkey brain reorg to VQ (human amputee(

- They used magnetoencephalography (MEG) to map the representation of the body in somatosensory cortex: − Similar to the deafferented monkeys, upper arm and face areas of cortex enlarged occupying what used to be the hand area.

Can the maps reorganize in response to an increase in sensory input? and Do motor representations also undergo reorganization?

- YES and YES

can we do anything to direct the plasticity (ie to aide in recovery)

- YES, Evidence that retraining following brain damage induces reorganization in motor cortex and improves functional recovery

neurogenesis is affected (positively and negatively) by such variables

- as exercise (+), drugs (-), enriched environments (+), depression (-), stress (-).

neuroplasticity occurs when in life

- both rewiring and neurogenesis occurs throughout the lifespan from prenatal to senescence (aging)

Neuroplasticity refers to the ability of the nervous system to

- change EITHER in form or function

Recent studies demonstrated adult brain reorganization based on

- changing sensory input and motor output

Discoveries about neuroplasticity & neurogenesis in the adult have revolutionized our understanding of

- how the brain works

neurogenesis info

- ie the generation of new neurons from precursor cells (occurring throughout the lifespan)

Neuroplasticity following widespread and long-term denervation results in what and eg

- massive cortical reorganization --> eg the Silver Spring monkeys (Edward Taub)

Silver Spring monkeys (Edward Taub) - results 12 yrs later

- neurons that formed cortical representation of the arms and hands now receive signals from the face --> ie tactile stim in the face caused activity in neurons that used to be for the hand and arm area **notice how much larger the face is

2 aspects of neuroplasticity in the adult - list

- rewiring and neurogenesis - these 2 demolished the previous dogma about the adult brain

Neuroplasticity in somatosensory cortex: most experiments demonstrating cortical plasticity have been carried out in

- somatosensory cortex where there is topographic representation

Cortical artery occluded in squirrel monkeys to destroy only a small portion of the cells in primary motor cortex controlling the hand and digits. The recovery of hand function, AND reorganization pattern in motor cortex, depended on whether the monkeys received 'rehab' (info)

- some = where left alone - some = rehabed --> ie forced to use their bad arm/hand (taub's technique) and were trained to retreive food from smaller food wells

Understanding the mechanisms of reorganization in cortex following input changes has important implications for rehabilitation of patients who have had (2)

- strokes and other forms of brain damage

constraint induced movement therapy (CIMT) by TAUB - outcomes (2)

- • Improved use of paretic hand • Use-dependent cortical plasticity demonstrated with electroencephalography - EEG

Until recently the widely accepted dogma was that in the adult human brain the connections are fixed - thes lead to the goal of caring rather than curing,,,,... This dogma made sense based on (2)

ecovery of function seen following CNS damage in children compared to adults (e.g. recovery from aphasia -- there is little recovery from aphasia in adults but kids will regain language fx) - • laboratory studies that demonstrated a limited time during development when sensory experience could change brain organization, called CRITICAL PERIODS (e.g. binocular cells in visual cortex --- depend on input from the 2 eyes during dev, if 1 eye is deprived there will be no binocular neurons BUT NOT IN ADULTS) ***these 2 made us think that we can't fix damage to the brain***

Neuroplasticity on a much broader scale - braille reading for blind and deaf people egs/infos (congenitally blind and deaf)

• Visual cortex is activated during braille reading in congenitally blind people as recorded by PET and fMRI --> and disabling visual cortex using transcranial stim interferes with ability to read in blind!!!! • Auditory cortex in congenitally deaf people is activated by peripheral visual stimuli --> and behavioral responses are quicker

Recent experiments have demolished the dogma of car not cure via (2)

• evidence for reorganization (re-wiring) of existing circuits (that occurs post-injury) • evidence for neurogenesis in adults

based on the monkey trials what therapy have we come up with for humans with brain damage from stroke etc

In humans with brain damage, a form of rehabilitation therapy called constraint induced movement therapy (CIMT) by TAUB **contrain the arm, force the other to be used**

Silver Spring monkeys (Edward Taub) - expt did what (3)

− Initial experiments looked to see if monkeys could be 're-educated' to use a deafferented limb − Underwent dorsal rhizotomy (C2 - T4) − PETA members 'kidnapped' monkeys − 12 years later... neurons that formed cortical representation of the arms and hands now receive signals from the face.

Neurologists (e.g. Ramachandran) wondered whether animal experiments on sensory map reorganization could shed light on his theories about (2)

➢ phantom limb sensations ➢ plasticity of the 'body image'