Investigating the brain’s functional anatomy post burn injury using transcranial magnetic stimulation (TMS)

[Truncated] It is known that the brain’s functional anatomy is able to reorganise itself in response to injury. What is yet to be described is how the brain will reorganise itself in response to a burn injury, and whether this reorganisation persists over time. This is among the first studies to investigate the cortical response to a burn injury. The secondary aim of this study was to establish if transcranial magnetic stimulation (TMS) is a sensitive methodof measuring the cortical response to a burn injury.

To date, many burns studies have focussed on local aspects of wound healing, as these have been shown to improve aesthetic and functional outcomes through better wound healing (Greenhalgh, 2007) (Giles et al., 2007). Indeed, the scar that results from a burn is the most often the cause of the aesthetic and physical complications associated with burn wound healing (Serghiou et al., 2002). However, recent studies suggest that following burn injury to the peripheral nerve field, repair may be driven by the central nervous system (CNS) and not just a local response (Morellini et al., 2012, Anderson,2007).

Previous studies have demonstrated the plasticity of the motor cortex in response to peripheral injuries. This includes injuries such as amputation, nerve block, or pain (Chen, 2002). This study addresses the question of whether these changes also occur in response to a burn injury.

This study revolves around three main aims:

To establish whether there is a persistent cortical response post burn injury.

To create a standard protocol for the use of TMS to investigate burns patients.

To investigate what effect, if any, that exercise may have on neuroplasticity.

In order to investigate the first aim, both burn injured and uninjured subjects were recruited to undergo testing. For investigation of corticomotor pathways, all subjects underwent TMS testing. I chose TMS to conduct this testing as it is a useful tool for investigating the CNS (Hallett, 2007). It is a non-invasive tool, which we used to map the motor cortex, as well as analysing various components of the responses to TMS, which provides information regarding cortical excitability and inhibition (Hallett,2007). The burns patients underwent more comprehensive testing, which included sensory testing. They also completed functional quality of life and disability questionnaires, which provided an insight into their own perceptions regarding theoutcome of their injury.

The data looked at each patient individually and comprehensively. As a burn is a highly variable injury, with respect to factors such as severity, depth, extent, and outcome, the burns patients with different injury characteristics were then compared with each other, as well as with the uninjured subjects tested.

The results of this study have revealed that there is a cortical response to a burn injury. It was found that the position of the centre of cortical representation is in a significantly different position on the cortex for the burn injured arm of the patients tested when compared to the uninjured subjects that were tested. It was also noted that the total area of representation of the muscle tested in the burn arm of these patient was smaller compared to the uninjured subjects; however, this result was not statistically significant.

Further analysis using the TMS data provides insight into the processes that are occurring at the neuronal level in response to the burn injury. It was found that there is a reduction in intracortical inhibition, as indicated by a shortened silent period duration,and an increase in intracortical excitability, as indicated by a reduced stimulus threshold and increased motor evoked potential (MEP) amplitude in the burn arm of patients withparticular burn characteristics.