The capacity of the human brain to recover and rewire itself peaks around two weeks after a stroke and diminishes over time, found a small international study.
The finding is the result of a study in London and Adelaide that followed the recovery of 60 stroke patients up to one year after their stroke.
Lead author Dr Brenton Hordacre, from the University of South Australia, says the multi-site study showed conclusive evidence that the brain only has a small window of opportunity to more easily repair itself after stroke.
"Earlier animal studies suggested this was the case, but this is the first time we have conclusively demonstrated this phenomenon exists in humans," Hordacre says.
The researchers scanned the brains of stroke survivors as they recovered over 12 months. They found that in the initial days following an ischemic stroke (caused by a blocked artery to the brain), the brain has a greater capacity to modify its neural connections and its plasticity is increased.
"It is during this early period after stroke that any physiotherapy is going to be most effective because the brain is more responsive to treatment.
"Earlier experiments with rats showed that within five days of an ischemic stroke they were able to repair damaged limbs and neural connections more easily than if therapy was delayed until 30 days post stroke."
The researchers used continuous transcranial magnetic stimulation (cTBS) to repetitively activate different hemispheres of the motor cortex to measure brain plasticity.
The Adelaide laboratory tested the stroke damaged motor cortex, which is the main area that controls movement. The London laboratory tested the non-stroke damaged hemisphere which is also important to help recovery.
"Our assessments showed that plasticity was strongest around two weeks after stroke in the non-damaged motor cortex. Contrary to what we expected, there was no change in the damaged hemisphere in response to cTBS."
Hordacre says the findings confirm the importance of initiating therapy as soon as possible after a stroke.
Current evidence indicates that less than eight minutes of daily therapy is dedicated to upper limb recovery within the first four weeks of a stroke.
"Delivering more treatment within this brief window is needed to help people recover after stroke.
"The next step is to identify techniques which prolong or even re-open a period of increased brain plasticity, so we can maximise recovery," Hordacre says.
Evidence for a Window of Enhanced Plasticity in the Human Motor Cortex Following Ischemic Stroke
Brenton Hordacre, Duncan Austin, Katlyn E Brown, Lynton Graetz, Isabel Pareés, Stefania De Trane, Ann-Maree Vallence, Simon Koblar, Timothy Kleinig, Michelle N McDonnell, Richard Greenwood, Michael C Ridding, John C Rothwell
Published in Neurorehabilitation and Neural Repair on 12 February 2021
In preclinical models, behavioral training early after stroke produces larger gains compared with delayed training. The effects are thought to be mediated by increased and widespread reorganization of synaptic connections in the brain. It is viewed as a period of spontaneous biological recovery during which synaptic plasticity is increased.
To look for evidence of a similar change in synaptic plasticity in the human brain in the weeks and months after ischemic stroke.
We used continuous theta burst stimulation (cTBS) to activate synapses repeatedly in the motor cortex. This initiates early stages of synaptic plasticity that temporarily reduces cortical excitability and motor-evoked potential amplitude. Thus, the greater the effect of cTBS on the motor-evoked potential, the greater the inferred level of synaptic plasticity. Data were collected from separate cohorts (Australia and UK). In each cohort, serial measurements were made in the weeks to months following stroke. Data were obtained for the ipsilesional motor cortex in 31 stroke survivors (Australia, 66.6 ± 17.8 years) over 12 months and the contralesional motor cortex in 29 stroke survivors (UK, 68.2 ± 9.8 years) over 6 months.
Depression of cortical excitability by cTBS was most prominent shortly after stroke in the contralesional hemisphere and diminished over subsequent sessions (P = .030). cTBS response did not differ across the 12-month follow-up period in the ipsilesional hemisphere (P = .903).
Our results provide the first neurophysiological evidence consistent with a period of enhanced synaptic plasticity in the human brain after stroke. Behavioral training given during this period may be especially effective in supporting poststroke recovery.
Neurorehabilitation and Neural Repair study (Restricted access)
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