Transcranial Magnetic Stimulation Analysis - Dissertation Example

?Discussion The results of this study show that in the Mu values of the right and left eye in the three anti-saccade performances for all four s were similar to each other. These results confirm a significantly low degree of variability in the three anti-saccade task performances (correct response in each task). Mu and Sig values were observed for both left and right eye movements in the three anti-saccade tests for each participant. The Mu and Sig value results of all the participants were convergent, which also indicates that the degree of variability in the three anti-saccade task performances was significantly low, with the exception of the right eye movement Sig value for the fourth participant and the left eye movement Sig values for the second participant. This indicates slight differences between the Mu and Sig values of the three anti-saccade tests. The aforementioned results provided important and meaningful quantitative information regarding the shapes of the distributions. The participants had a convergent performance in the three anti-saccade tasks. Consequently, it can be verified that the anti-saccade task design was sufficiently stable and any alteration in the average of correct response time was due to other factors such as TMS effect (Wassermann et al., 2001) or ADHD state (Leth-Steensen et al., 2000). Questionnaires are accessible to consider a childhood history of ADHD symptoms, as conveyed by the patient or by parents or adults who knew the patient as a child (Solanto, 2011). It is crucial to accentuate that an ADHD questionnaire austerely determines the patient’s supposed level of present intricacies in the realms of attention, disorganization, impulsivity, executive dysfunction, hyperactivity and other symptoms in comparison to what is experienced by adults in the population at large. However, the results obtained in such questionnaire cannot unleash anything about the source or basis of these complexities experienced by the participant. In order to determine the appropriate diagnosis for ADHD state, clinicians need to tailor their methods depending on the time and resources available to them (Barkley, 2006). However, all evaluations should attempt to address the four questions centred on adult ADHD evaluation inattention, hyperactivity, impulsivity and sluggish cognitive tempo. Furthermore, examiners may wish to utilise a comprehensive, practical and easy-to-use set of interviews and rating scales (Barkley, 2006). Indeed, the results of a study conducted by Etefia, Solanto and Marks (2004) showed that patients experiencing anxiety and depression, but for whom ADHD had been ruled out, received scores in the inattentive aspect of the questionnaire that were as high or higher than those patients diagnosed with ADHD. This result signifies that internalizing disorders may be related with a level of inattention, disorganization and poor time management that is equivalent to what is experienced by adults with ADHD (Solanto, 2011). Thus, it is essential for clinicians to ascertain the onset and chronology of these symptoms and specifically, their association to internalizing symptoms in order to clarify whether they denote the existence of ADHD or another disorder. Attention-deficit hyperactivity disorder as stressed by Klein et al. (2006) is a frequent disorder of childhood and adolescence. The diagnosis of ADHD concentrates on the symptom domains of inattention and impulsiveness or hyperactivity (Klein et al., 2006); hence, it is crucial to determine any significant differences in the inter-individual and intra-individual variability in the ADHD current state for clinicians to better classify and diagnose what a participant is manifesting. Likewise, in this study, the important variances in ADHD state were considered in order to differentiate one from the other. It is crucial to determine the number of ADHD symptoms endorsed both currently and retrospectively during childhood (Barkley, 2006). The symptoms possessed by the participants vary in terms of inattention, hyperactivity and impulsiveness. Likewise, the degree of the severity of the symptoms differs extremely, although some participants did not exhibit any symptoms. In support of these findings, Etefia et al. (2004) found that when individuals are asked questions regarding their perception of their symptoms, there is a significant difference when discussing each symptom. However, the cause and co-morbidities of such symptom is difficult to undermine. The majority of the results obtained showed no significant effect of theta-burst TMS on the participants’ performance on the anti-saccade tasks except when the time points are being considered. It is most likely that such effect was noted due to the reason that the anti-saccade design was too lengthy, 3 tests and 300 trials in each test, that lead to the exhaustion of the participants. It is well known that the brain selectively processes incoming visual images, enhancing relevant parts (Neggers et al., 2007). The study by Neggers et al. (2007) provided evidence that the FEF are responsible for this coupling between eye movements and shifts of visuospatial attention which is in contrast to what was discovered in the effect of TMS in this study performed. Thus, further research is required to determine the role played by FEF in the coupling between eye movements and shifts of visuospatial attention. In a study conducted by Triggs et al. (1999) entitled, Transcranial Magnetic Stimulation Identifies Upper Motor Neuron Involvement in Motor Neuron Disease, it evaluated the sensitivity of transcranial magnetic stimulation or TMS to identify upper motor neuron involvement in patients with motor neuron disease. In the said study by Triggs et al. (1999), TMS revealed evidence of upper motor neuron dysfunction in 84 out of 121 patients which is equivalent to 69%, comprising 30 of 70 patients or 75% with only probable upper motor neuron signs and unsuspected motor neuron involvement in 6 of 22 patients or 27% who had purely lower motor neuron syndromes clinically. Based on the results obtained, Triggs et al. (1999) concluded that TMS provides a sensitive means for the assessment and monitoring of excitatory and inhibitory upper motor neuron function in motor neuron disease. In another study conducted by Vucic and Kiernan (2006) entitled, Novel Threshold Tracking Techniques suggest that Cortical Hyperexcitability is an Early Feature of Motor Neuron Disease, aimed in applying novel threshold tracking Transcranial Stimulation or TMS techniques in conjunction with peripheral nerve excitability studies in Motor Neuron Disease or MND patients to further investigate the dying forward hypothesis of MND which suggests that corticomotoneurons induce excitotoxic anterior horn cell death, with involvement of the glutamatergic neurotransmitter system; and to possibly determine the site of disease onset. Studies were undertaken in 23 MND patients using a 90-mm circular coil connected to a BiStim magnetic stimulator for cortical studies and electrical stimulation for peripheral nerve excitability studies (Vucic & Kiernan, 2006). Motor-evoked potentials and compound muscle action potentials (CMAPs) were recorded by Vucic and Kiernan (2006) from the right abductor pollicis brevis in the same setting. Measures of cortical and peripheral nerve excitability were correlated by Vucic and Kiernan (2006) with clinical and neurophysiological parameters of disease severity. Vucic and Kiernan discovered that short-interval intracortical inhibition (SICI) was significantly reduced in MND patients compared with controls (MND group = 3.6 ± 0.8%; controls = 8.5 ± 1.0%, P < 0.001), most prominently in MND patients with limb-onset disease. Vucic and Kiernan (2006) also noted that changes in intracortical inhibition were accompanied by alterations in the magnetic stimulus–response curve, cortical silent period duration and resting motor threshold, all indicative of cortical hyperexcitability. Furthermore, although the reduction in SICI was more pronounced in MND patients with less severe disease, as assessed by the CMAP amplitude, it remained evident even in MND patients with advanced disease (Vucic & Kiernan, 2006). Measures of peripheral disease burden, namely the CMAP amplitude (r = ?0.6) and neurophysiological index (r = ?0.6), correlated with cortical hyperexcitability changes, as did the strength-duration time constant (r = ?0.6), a peripheral marker of axonal excitability was also noted by Vucic and Kiernan (2006). Hence, Vucic and Kiernan (2006) concluded that simultaneous assessment of central and peripheral nerve excitability has established the presence of co-existent upper and lower motor neuron dysfunction, with cortical hyperexcitability which is an early feature in MND. With the results obtained from the aforementioned studies and this study presented the significance of TMS and its impact on the neurons of the brain. Likewise, it also illustrated the crucial importance of TMS in aiding the diagnosis of certain conditions such as motor neuron disease. In attempting to answer whether GV and GA was affected by TMS in lieu of what the respondents perceived, the aforementioned tasks in this study were conducted. The results showed that there was a significant difference in the GV scales in contrast with the GA measure which exhibited no significant difference. Monk (1989) reported remarkable changes in the GV scales, in contrast to GA measures, which provided insignificant differences. However, the study conducted by Monk (1989) focused on assessing the state of emotions of the participants before and after undergoing varied circumstances to show, for instance, if a certain condition may contribute valuably to the person or, in opposition, may be detrimental to that individual. The similarity of the findings of the present study with the study conducted by Monk (1989) is that there was a significant difference in the GV scales in contrast with the GA measure which presented no significant difference; hence, it can be stated that TMS had a notable influence on GV scales in comparison with GA measures. The significant correlations of the participants’ symptoms vary in terms of inattention, hyperactivity, sluggish cognitive tempo, impulsiveness and overall ADHD. The said scales denote whether relation is minimal, moderate or severe. This may be due to the degree of severity of the ADHD symptoms may have been recently greater with some participants compared to the others. It could be attributed to the fact that some of the participants already possessed ADHD symptoms. It is also possible that some concealed symptoms may have been stimulated by a variety of factors that confronted the participants. It can be depicted that it was likely that the participants are experiencing ADHD symptoms but they are simply unaware of those or it can be compared with a dormant volcano not erupting for years but with a strong stimulus, it awakens and erupts just like with the symptoms obscured in the individuals, the stimuli brought about by the factors induced by the study may have provoked the presentation of hidden symptoms. In a similar study, the anti-saccade task was utilized as it requires participants to inhibit the reflexive tendency to look at a sudden onset target and instead direct their gaze to the opposite hemifield (Tatler et al., 2006). Hence, it provides a convenient tool with which to investigate the cognitive and neural systems that support goal-directed behaviour, such scheme was also the one employed in the fulfilment of this study. There are a number of limitations of the study. In comparison a similar study, the number of sessions provided to the participants in this study was considerably lower. For example, in the study by Akaishi et al. (2010), the participants were tested during 10 or 12 sessions in contrast with the 2 sessions that were given to the participants of this study. Two sessions may not have been enough to collect sufficient data. In addition, the theta burst TMS was stimulated at 50% of the active motor threshold while most of participants in this study had a threshold stimulant point of approximately 80%. Therefore, 50% of the active motor threshold may be too low for significant results to be observed. However, ethical approval for the theta burst TMS to be stimulated at 80% was not in likely at the time of the study. Therefore, low intensity TMS used in this study did not affect the performance of the subjects. However, in previous studies on human participants, TMS on the FEF did not induce a significant effect on the eye movements even with maximum stimulator output (Muri et al., 1991; Wessel and Kompf, 1991). In conclusion, the findings of this study suggest that individuals possess variances with regards to the manifestation and severity of ADHD state. There is truly a remarkable inter and intra-individual variability in the current ADHD state, which is a crucial undermining factor that must be considered when diagnosing and treating ADHD. Furthermore, there is no significant influence induced by TMS on the participants’ performance on all the factors presented, such as the intensity of the employed TMS except when time points are being considered that obtained a negative influence as a result of the exhaustion and weariness on the side of the participants, which is brought about by lengthy time intervals between tasks. GV was significantly affected when the study participants are confronted with TMS, in contrast with GA, which evidently showed no alterations when the study participants are faced with TMS. Finally, there are significant differences in terms of correlation of predisposing factors to ADHD symptoms. The following recommendations are given emphasis based on the findings of this study. It is recommended that a more thorough study be conducted to better enhance the findings obtained in this research. Future researchers are encouraged to utilize more sessions with short time intervals to avoid participant exhaustion and for prospective studies to endeavour at employing a higher level of TMS, as allowed by a designated Ethical Committee, without compromising the welfare of its study subjects. Additional References Triggs, W.J., Menkes, D., Onorato, J., Yan, R.S.H., Young, M.S., Newell, K., Sander, H.W., Soto, O., Chiappa, K.H., & Cros, D. (1999). Transcranial Magnetic Stimulation Identifies Upper Motor Neuron Involvement in Motor Neuron Disease. Neurology, 53 (3), 605. Vucic, S., & Kiernan, M.C. (2006). Novel Threshold Tracking Techniques suggest that Cortical Hyperexcitability is an Early Feature of Motor Neuron Disease. Brain, 129 (9), 2436-2446. Read More