Experimental setup and procedure
Discuss About The Mental Rotation Requires Short Term Memory.
Single-pulse TMS has been used in research in various different ways. TMS impulse in certain region of the cortex can disrupt cognitive functionality (Eisenegger, Herwig&Jäncke, 2007). The method has been providing a better way for testing of causality compared to other methods that makes use of correlations based study. An important human brain function is to be able to develop and manipulate mental images. In order to understand this psychological cognitive function Shepard and Metzler innovated rotation technique for creating effects of visual imagery observable. Their study involved analysing linear positive images by rotating them at various degrees to be able to understand disparity between them. Analysing images obtained from mental manipulation, it was understood that it follows similar pattern compared to objects in physical world. Neuroscience research since a long period of time had use of mental imagery (Bode, Koeneke&Jäncke, 2007). When results were obtained using functional magnetic resonance imaging (fMRI)it was derived that parietal cortex is involved in mental rotation process. Several researchers conducting study in the field examined whether motor skills were indulged in mental rotation process. Evaluation of theoretical concepts helped arrive at dynamic imagery and overt movements relying on neutral networks. There was debatable consideration over whether primary motor areas are directly linked to mental rotation(Kalbe et al, 2010). Human primary motor cortex in mental rotation of body parts had said to come from two transcranial magnetic simulation (TMS) studies. TMS was externally applied on right hand and left hand areas with mental rotation being performed of the pictures of hands and feet. The study reflected slowing of response time when TMS pulse was applied at 400 ms or 650 ms. Studies conducted, reflects specifically areas that is responsible for mental rotation (Milivojevic, Hamm &Corballis, 2009). More developed studies that deeper findings that reflected TMS having no direct influence on mental rotation. However, there is a scope for analysing if at all TMS real and sham can cause any difference in mental cortex. The scope of this study aims at filling the literature gap by experimenting and understanding whether there is a difference in response time between real TMS and sham TMS when participant is shown hand figure and Shepard figures (geometrical shapes)
There were two experimental setups for the study and two null hypotheses were assumed for the purpose. It was hypothesized that primary motor cortex (M1) was not significantly associated with mentally rotating external objects, and primary motor cortex (M1) was also not significantly associated with mentally rotating hands. These hypotheses were tested against the alternate hypotheses where the association of primary motor cortex (M1) was positively associated with mentally rotating external objects and mentally rotating hands. Positive association signifies the reduction in response time (RT) for the experiments.
The current study was a fictive follow-up on two mental rotation studies making use of TMS as has been by stated Eisenegger et al (2007) and Bode et al (2007).
For the purpose of the experiments participation was invited from the students of the university. Students were distributed with handouts mentioning the detailed experiment structure of the study and reasons for the study. Total 50 students expressed interest for the purpose of the study. A workshop was conducted by study coordinator and students were briefed in details about the two experiments of the research work. Left-handed participants were excluded for the purpose of the study. Students with low vision and psychological and neurological disorders were also excluded for the purpose. Proper reasons were justified to them. At the end of the workshop total 30 participants were chosen who were all right handed and with normal or corrected-to-normal vision. All of the participants were made to read the ethical form of the work which was approved by the ethical committee of the university and they were assured that collected results of the two experiments will be used for the purpose of the study. Participants went through the debrief sheet after their final selection. Participants were aged between 19 years to 25 years and the average age of the participants was 23. Equal number of male and female candidates was present in the sample group.
The experiment was performed with the help of ‘Transcranial Magnetic Stimulator’ machine. Magnetic resonance pulses were sent to the brain of the participants to analyse the effect of sham TMS compared to real TMS. Random pulses were made to pass through the participant’s brain during mental rotation over left M1. Real TMS pulse was applied in the even blocks of the brain and sham TMS was applied in the odd blocks. The following figure describes the model. The task was identical to the TMS part in Bode et al. (2007).
All the participants were asked to ease out in the lobby of the laboratory. The two experiments, Hand’s study and Shepard’s study were performed with the entire group of candidates. The eight-shaped coil of the TMS was fitted on the scalp of every participant to read the impulse signal from the brain. The subjects of the study were positioned in front of the computer monitor screen precisely as explained in Bode et al., 2007. Initially they were shown different images of the same objects and their response time was noted. Afterwards they were shown hand positions in different angles. Participants were asked to press a response button and the response time of the subjects was recorded accordingly.
The experiment started with the Shepard’s study and the subjects were shown objects from various angles. Six different angles were used for the purpose, but images of the same object were used. The response time for real TMS over the left hand area of M1 was noted, later the sham TMS response time got recorded (Bode et al., 2007). The participants were allowed a break of 20 minutes. In the second half, picture of hands were exhibited from different angles and response time for real TMS was taken. Later, response time of the subjects for hand study was noted with sham TMS pulses.
The descriptive values of the response time across all the real and sham TMS blocks were to be calculated. The average response time of the subject along with the standard deviation indicated the overall scenario of the study. To compare the real TMS and sham TMS condition of a subject and check the difference in the two scores for both the experiments paired t-test was the appropriate choice of test considering the Gaussian nature of the population.
The first hypothesis was based on Shepard’s experiment and a one-tailed paired t-test was performed to test the association between the real and sham TMS situations. The nature of disparity of the mental scores got explained by the results. The t value was 3.84 with significance level (p-value) less than 0.05. Therefore the alternate hypothesis was accepted and the significant positive effect of sham TMS compared to real TMS was observed for Shepard’s experiment. The response time to analyse and recognize the pictures decreased in sham TMS condition. The average difference in response time was 164.9 ms with S.D of 235.3 ms. The effect size of the sample from Cohen’s D was 0.7 which was in the large effect size group.
The second hypothesis was based on Hands experiment and again a one-tailed paired t-test was performed to test the association between the real and sham TMS situations. The t value was 3.30 with significance level (p-value) less than 0.05. Therefore the alternate hypothesis was accepted and the significant positive effect of sham TMS compared to real TMS was observed for Hand’s experiment. The response time to analyse and recognize the different hand positions decreased in sham TMS condition. The average difference in response time was 125.17 ms with S.D of 207.88 ms. The effect size of the sample from Cohen’s D was 0.6 which was in the medium effect size group.
The study has assumed in its hypothesis that primary motor cortex (M1) is causally involved in mentally rotating external/objects. Secondly, primary motor cortex (M1) is causally involved in mentally rotating hands. The assumption of null hypothesis is appropriate as it does not establishes any connection between primary motor cortex (M1) with that of mentally rotating external objects or hands(Munzert, Lorey&Zentgraf, 2009). Literatures in studies that have been developed been developed in the past indicates mental rotation of standard Shepard & Metzler figures is known to excite left primary cortex region demonstrated by enhanced MEPs of the APB of right hand. Earlier studies therefore depicts that cortex is associated with mental rotation of objects or hands. However, these studies conducted did not include experiments conducted with real TMS and sham TMS. There was a limitation associated with the studies that was conducted as participants were observed for their excitement in cortex region(Prime &Jolicoeur, 2010). This study hence aims at understanding relation between response timing when real TMS is subjected as against sham TMS. Such application of sham TMS, in case of positive results were obtained could provide course for further studies in neurological sciences. Moreover, increased response rates that have been studied in this experiment could pave way for treatment of various neurological or mental disorders.
The scope of current experiment has proved to be an extension to previous studies that has been developed in the field. Researchers till now had focused on analysis of connectivity between mental rotation and excitement of cortex region, as proposed by Eisenegger, Herwig and Jancke (2007). Another study by Windischberger, Lamm, Bauer and Moser (2003) was studied similar functions of the cortex. They analysed areas or regions of the brain that is responsible for generating stimulus (Pelgrims et al, 2011). Study by Bode, Koeneke and Janke (2007) evaluated cognitive functionalities of the brain. They analysed that apart from left cortex of the brain, there are other areas adjacent to left cortex that are responsible for generating stimulus. This study provides a whole new dimension by analysing differences between Sham TMS and Real TMS application on the cortex region. Relating to results from previous findings, it can be said that left cortex is responsible for mental rotation. Current findings are based and developed on previous literatures and findings with greater areas for applicability(Tomasino et al, 2008). Findings from current study reflects that sham TMS has significantly effect on the response time by reducing it as compared to the real TMS. In both the studies of hand test and Shepard tests where participants being subjected to real TS versus sham TMS demonstrated significant differences in their response times(Zacks,2008).
Limitations of this study are that from Cohen’s D effect size of the sample was not significantly large enough for establishing the results.
Future direction of such studies needs to include greater sample size such that results of the studies can be established in a better manner to include response timing.
Drawing conclusion from the above experiment, there can be two prominent inferences made. Firstly cortex is excited on mental mirroring. Secondly, Sham TMs can generate lesser response time compared to real TMS.
Bode, S., Koeneke, S., &Jäncke, L. (2007). Different strategies do not moderate primary motor cortex involvement in mental rotation: a TMS study. Behavioral and Brain Functions, 3(1), 38.
Eisenegger, C., Herwig, U., &Jäncke, L. (2007).The involvement of primary motor cortex in mental rotation revealed by transcranial magnetic stimulation. European Journal of Neuroscience, 25(4), 1240-1244.
Kalbe, E., Schlegel, M., Sack, A. T., Nowak, D. A., Dafotakis, M., Bangard, C., ...& Kessler, J. (2010). Dissociating cognitive from affective theory of mind: a TMS study. cortex, 46(6), 769-780.
Milivojevic, B., Hamm, J. P., &Corballis, M. C. (2009).Functional neuroanatomy of mental rotation. Journal of Cognitive Neuroscience, 21(5), 945-959.
Munzert, J., Lorey, B., &Zentgraf, K. (2009). Cognitive motor processes: the role of motor imagery in the study of motor representations. Brain research reviews, 60(2), 306-326.
Pelgrims, B., Michaux, N., Olivier, E., & Andres, M. (2011). Contribution of the primary motor cortex to motor imagery: a subthreshold TMS study. Human brain mapping, 32(9), 1471-1482.
Prime, D. J., &Jolicoeur, P. (2010). Mental rotation requires visual short-term memory: Evidence from human electric cortical activity. Journal of Cognitive Neuroscience, 22(11), 2437-2446.
Tomasino, B., Fink, G. R., Sparing, R., Dafotakis, M., & Weiss, P. H. (2008). Action verbs and the primary motor cortex: a comparative TMS study of silent reading, frequency judgments, and motor imagery. Neuropsychologia, 46(7), 1915-1926.
Windischberger, C., Lamm, C., Bauer, H., & Moser, E. (2003).Human motor cortex activity during mental rotation. NeuroImage, 20(1), 225-232.
Zacks, J. M. (2008). Neuroimaging studies of mental rotation: a meta-analysis and review. Journal of cognitive neuroscience, 20(1), 1-19.
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