Movement Intention after Parietal Cortex Stimulation in Humans. Essay Example.

The motor responses and coordination are controlled in the premotor and parietal regions of the brain. The two brain segments bring about awareness as the body responds to the electrical signals that trigger movement of the different body parts. Desmurget et al. (2009) carried out a scientific inquiry to establish the relative change in the movement intention in humans after the parietal cortex simulation. In their study, they employed a study sample of seven patients and used electrical stimulation of varying intensity. The patients behavior was analyzed in two different perspectives about the parietal sides and the premotor region the electrical simulation was located. The movement intention of the body changes relatively depending on the intensity of electrical stimulation and the exact part the signal hits as examined in this paper.

Many people are always concerned with knowing the part of the human brain that forms the center for human intentions and how the intentions are recognized in the body. The dualist philosophy indicates that the mind is the crucial organ in the mental apprehension of an object or action (Purves, 2011). However, some researchers have brought their arguments relating to the conscious intentions in the spiritual aspect, but their opinions lagged behind. From the study findings, most researchers agree that the voluntary movement occurs as a result of nerve impulse transmission in the premotor-parietal circuit (Nieuwenhuys, 2012). This explains that before an action is done, motor signals are recognized and interpreted by the brain. The motor awareness concept is also linked to the cortical circuit (Desmurget et al., 2009). However, there has been a research gap to explain the contribution of parietal and premotor regions in recognition of conscious intentions and motor awareness in the human system.

As a result of the research gap, Desmurget et al. experimented to establish the link that existed between the movement intention and the parietal stimulations. The team of scientists hypothesized that they could evoke motor responses by directly applying stimulation signals to the premotor and parietal cortex regions. The sample they selected to work on comprised of seven patients suffering from brain tumors and the variable for the experiment was the direct electrical stimulation signals (DES). The stimulation sites targeted were three, and this includes the posterior segment, the anterior segment, and the central locus (Desmurget et al., 2009). The DES was used as the tracking technology to observe the behavioral changes in the patients after subjection to local anesthesia during the operation. This method proved to be useful as it reduced the complications associated with postoperative sequelae. For each patient, four distinct replications were conducted for each stimulation site (Krebs & Akesson, 2011). The DES used was bipolar and the standard electrode intensities and specific time durations adhered to during the experiment. It is worthwhile noting that the replications procedures were done randomly to prevent provoking seizures.

The electromyography (EMG) signals were collected as the experiment was running. The signals obtained included the 12 muscles that are located in the foot, wrist, face, knee, hand, and elbow. The peri-operative neuron navigation system detected the high-resolution magnetic resonance (MR) signals showing the confined stimulation sites. The signals detected were then recreated in the offline mode. The number of stimulates sites in the parietal, temporal, and frontal regions was fifty-seven. The Brodmann areas (BA) 7, 39, and 40 were the parietal simulation sites for the posterior simulation (Desmurget et al., 2009). For the premotor region, the simulations were conducted on the dorsal segment of the sixth Brodmann area. However, the mesial structures linking the supplementary motor area (SMA) and the convexity were left aside in the experiment.

From the experimental set, up the researchers obtained unique results and analyzed them using computational manipulations. Forty-six percent of the stimulated sites were observed to be silent. This shows that the DES did not trigger any sensations on the signals on the motor responses. The twenty percent of the motor responses were connected to the somatic sensations for instance itching or tingling. The Sixteen percent of the remaining portion indicated that the evoked responses were associated with movement intention or motor cognizance. The 18% left proved that the actual movements were as a result of movement intentions. Nine responsive sites were detected in BA 39 and 40 for the case involving three patients suffering from post-central cancers (Desmurget et al., 2009). The general observation indicated that an intention was produced as a result of stimulating the sites. This was evident in the EMG activity outcomes on the muscles involved in the experiment. It was also discovered that increasing the light intensity had no series effect on the perception of the movement.

The study report presented two conflicting results on the stimulation and movement intentions in humans. The first finding illustrates that the intention to move and to recognize the change in position is attributed to the stimulation of the posterior parietal cortex. This proves that the simulation happened or took place voluntarily without the influence of motor responses. The second finding explains the relationship between the mouth and limb movements and the premotor region (Krebs & Akesson, 2011). It was discovered that the mouth and limb movements in the patients happened as a result of premotor cortex region stimulation. However, some patients could not accept that they experienced the change, but in the real sense, it happened. The results shed light on the clinical remarks that link the parietal damage to the high levels of movement often observed in patients (Desmurget et al., 2009).

From the study results, there is a close link between body part movement and parietal cortex. The manipulations that are conducted in the parietal cortex region resulted in activated intention movement of the body parts. The patients expressed the desire to move from the initial locations. This shows that the stimulation not only induces a mental impression regarding movement but also triggered the intention to move (Desmurget et al., 2009). This observation further supports the theoretical hypothesis that was introduced by Searle referred to as intention in action. Also, the findings comply with the earlier observations recorded with non-human primates. According to the no-human primates study, the report indicated that the parietal cortex contained map of intentions that it controlled the various form of movements such as eye movement (Kuhlenbeck, 2013). Also, the parietal neurons activities were coordinated to facilitate the progressions in decision making that result from the motor planning. Additionally, from the study, it was evident that an increase in the electrical stimulation intensity resulted to illusory movement awareness instead of more vigorous motor intentions.

Moreover, another hypothesis describing the movement execution and cortical network can be formed from the observations. The patients admitted performing the movements that they desired to do initially even in the absence of muscle contraction. Therefore, from this view, it can be hypothesized that activation of the parietal cortical network increases the resultant signal transmission leading to the raises in the motor intention. This explains that stimulations of higher intensities not only raises the motor consciousness but also involves the executive network. The combination of the aspects is crucial in determining and monitoring the movement intentions in humans, primarily through the forwarding modeling. Posterior parietal computations data shows that the forward modeling depends majorly on the posterior parietal segment of the brain. The illusory movement observed in patients subjected to the higher electrical stimulation intensities could be as a result of the initial predictions suggested by the researchers on the BA 3, 4, 7, 24, and 25 (Desmurget et al., 2009).

The SMA also plays a vital role in the stimulation of the body movements. It was discovered that the feeling of the patients to involuntarily move past their desired target was due to the stimulation of the SMA. This explains how the motor intentions relate to the effects of SMA. The results from the patients gave a different conclusion on the link between the movement intentions and SMA as the patients had the desired to move generated endogenously. The motor intention is affected by the SMA stimulation as the higher current intensity prompted movements (Desmurget et al., 2009). The parietal stimulates sites exhibited the opposite effect as there were no evoked muscle contractions that resulted from the manipulation of the parietal segment. Therefore, the stage of at which stimulation is done matters a lot when it comes to the parietal part of the brain.

In conclusion, motor intentions are linked to both the SMA and the parietal cortex. However, the movement intentions in these two regions rely on the different stages involved in movement planning. SMA intentions are carefully directed to motor commands whereas the parietal cortex intentions are recognized relative to the sensory predictions. The premotor cortex is associated with the occurrence of complex stimulations often in the multi-joint movements. However, it is worthwhile noting that in some instances movements occur yet people are not in a position to detect. The study conducted by Desmurget et al. proves that the motor intention and awareness is due to the parietal activity that happens before movement execution.

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References

Desmurget, M., Reilly, K., Richard N., Szathmari, A., Mottolese, C., & Sirigu, A. (2009). Movement intention after parietal cortex stimulation in humans. Science, 324, 811-813. doi: 10.1126/science.1169896.

Krebs, C., Weinberg, J., & Akesson, E. J. (2011). Neuroscience. Philadelphia, Pa: Lippincott Williams & Wilkins.

Kuhlenbeck, H. (2013). The central nervous system of vertebrates: A general survey of its comparative anatomy with an introduction to the pertinent fundamental biologic and logical concepts. Basel: S. Karger.

Nieuwenhuys, R. (2012). The central nervous system of vertebrates: 1. (3rd ed.). Berlin: Springer.

Purves, D. (2011). Neuroscience. Sunderland, Mass: Sinauer.