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Explain the role of individual, psychological, and contextual factors on…
Explain the role of individual, psychological, and contextual factors on the neurophysiological effects of TMS
Transcranial magnetic stimulation (TMS) is a non-invasive brain stimulation technique that involves use of primary copper coil and electromagnetic current.
Barker et al (1985) introduced the first TMS stimulator and coil that could produce a motor response visible to naked eye
TMS involves use of a magnetic field generated by coper coil and this coil disrupts neuron electircal activity through inducing electrical current in areas of neuron actiivty within the brain, ((The Oxford Handbook of TMS 2008)
The surface of the brain contains many neuronal layers that are made up of inhibitory and excitatory neurons. TMS can stimulate different neurons to evoke different responses.
TMS involves knowing the motor threshold which is minimum stimulus intensity to produce motor-evoked potential (Libor Ustohal 2018)
Individual factors are differences between people that can affect their neurophysiology and TMS ouctomes. Individual factors can include age, sleep and cerebrospinal fluid volume.
Research conducted on 50 unique head models found that cerebrospinal fluid volume and brain-scalp distance correlated with lower intensity and increased spread of TMS, which suggests that anatomical differences can influence TMS outcomes (Lee et al 2018)
Research assessed effects of age on TMS outcomes. Research involved 42 healthy control subjects that were assessed in terms of active motor threshold, which is minimum stimulus intensity to produce liminal motor-evoked response in relation to isometric contraction of tested muscle at 20% maximum and resting motor threshold which is minimum stimulus intensity to produce liminal motor-evoked response at rest.
It was found that older people had higher active and resting motor thresholds, but there was no significant difference between younger and older people in terms of active and resting motor threshold.
Older people were found to have a shorter mean cortical silent period compared to younger people, which brings forward the idea that older people have more dysfunction to intracortical circuits compared to younger people (Oliveiro et al 2006)
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Individual factors can contribute to changes in neurophysiological structure of people, which can lead to different TMS outcomes and findings such as changes to brain structure and activity.
Psychological factors can be summarised as the influence of expectations on TMS findings and outcomes.
Psychological factors like expectations can influence numerous aspects of brain activity and influence TMS outcomes
TMS relies on the baseline activation of state regions and expectations can alter the state of the brain, therefore changing findings of TMS.
The dorsolateral prefrontal cortex is involved in expectations, attention and working memory and expectations can influence attention and working memory.
The activity of dorsolateral prefrontal cortex may be influenced by expectations, which causes changes in the way this brain area interacts with TMS (Braga et al 2021)
Expectations can influence neurophysiology through influencing brain states, and levels of activity within different brain areas, which can lead to different outomes in relation to TMS.
Contextual factors are factors such as the environment which TMS is taking place, whether patients have to travel to receive TMS and verbal and nonverbal patient-clinician interactions.
Contextual factors may influence psychological factors like expectations and cause changes to brain activity and states that alter TMS outcomes.
Contextual healing was an idea by Miller et al (2008) and it was suggested that factors in clinician-patient interaction may lead to patient healing and getting better. This theory is under-researched, making it difficult to pinpoint the role it may have in neurophysiology and TMS outcomes. More research into the idea of contextual healing could lead to additional way of utilising TMS and using context to influence outcomes.
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