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Cortical and Subcortical Contributions to Stop Signal Response Inhibition: Role of the Subthalamic Nucleus
Aron and Poldrack authored the article in the year 2006. The article revolves around the role of the subthalamic nucleus in stopping signal response inhibition through the aid of the cortical and subcortical contributions. The suppression of an existing response that has been initiated manually depends on the right part of the inferior frontal cortex. However, it is not clear on how the suppression function is carried out in the motor system. Suggestions regarding the subthalamic nucleus which is part of the basal ganglia play a crucial role in suppressing the response due to its placement, suppressing the direct frontal-striatal pathway which tends to be activated by the response initiation.
To investigate the role of the subthalamic nucleus, the researchers conducted two experiments in which they investigated the hypothesis with functional magnetic resonance imaging and stop-signal task. The subjects in these experiments responded to Go signals and as well attempted the inhibition of the initiated response to the occasional stop signals. In the first experiment, Going activated frontal, striatal, pallidal and motor cortical regions that are consistent with the direct pathway while at the same time stopping the activated right inferior frontal cortex and the subthalamic nucleus. Also, stopping the related activation was significantly greater for the fast inhibitors compared to the slow ones in both the inferior frontal cortex and the subthalamic nucleus. The activity in both inferior frontal cortex and the subthalamic nucleus regions was correlated across subjects.
In the second experiment, a high resolution functional and structural imaging was used to confirm the location of stopping the activation within the vicinity of the subthalamic nucleus. The researchers proposed that the role of the subthalamic nucleus was to suppress the thalamocortical output, thus blocking the execution of the Go response. The results of the experiments provide convergent data for a role for the subthalamic nucleus in stopping the inhibition of the signal response. The results also suggested that the speed of the Go and Stop processes had a probability of relating to the relative activation of the various neural pathways. There is a need for future research in order to establish whether the inhibition of the Stop-signal could be implemented through a direct functional neuroanatomic projection between the inferior frontal cortex and the subthalamic nucleus which is a hyper-direct pathway.
The research had various concerns regarding the limitations of neuroimaging as the activations by themselves cannot prove that a particular brain region is sufficient for a particular cognitive function. Besides, the interpretation of the activations is also limited by the relatively poor spatial resolution of the fMRI. However, the relatively spatial resolution in the first experiment was solved in the second experiment as the researchers used a high-resolution scanning. Another limitation of the article is that despite the use of the high-resolution scanning in the second experiment, the hypointense region on the T2-weighted structural scans did include two nearby areas that consisted high iron content that is the red nucleus and the substantia nigra. Due to this, it was impossible to ascertain that the activations were specific to the subthalamic nucleus rather than to the substantia nigra and the red nucleus. Despite the limitations in confidence that the activations of the inferior frontal cortex, subthalamic nucleus, pre-SMA and the GP are particularly related to inhibition, the research has some strengths in that there exists a strong convergent evidence from lesion, TMS and the deep brain stimulation studies that implicate the inferior frontal cortex and the subthalamic nucleus in the stop signal response inhibition.
The article is essential as it helps us in understanding how the brain works especially with the hypothesis whether the Stop signal response inhibition operates by the activation of the subthalamic nucleus in order to suppress the Go response. The results of the experiment provide new information that is important in regard to the functional neuroanatomy of cognitive control through the verification of the importance of the subthalamic nucleus for Stop-signal response inhibition as well as the suggestion that the Go and Stop processes could relate to the activation of various frontal/basal ganglia regions. Based on the results of the study, evidence that implicates the subthalamic nucleus with Parkinson’s disease has been found with patients suffering from the disease showing abnormalities in firing subthalamic nucleus tend to have SSRT deficits and thus tend to benefit from the stimulation of the subthalamic nucleus. Besides, patients also experience a faster SSRT in the event when their stimulus are on compared with off. Therefore, the research is significant not only to the researchers on Parkinson’s disease but also to the patients as they witness higher subthalamic nucleus firing.
The research is also significant in that it helps in understanding the various neurophysiological facts which have the probability of transcending the difference in effectors and this makes the study of crucial importance to neurologists. Some of the facts outlined in the study are that it shows the balance between the gaze-shifting and gaze-holding neurons in the frontal eye field determines whether a saccade is produced. Besides, the studies show that some of the neurons within the frontal eye field enact inhibition before the SSRT while others don’t. The frontal eye field possesses neurons which are responsible for the control of movement while the medial frontal regions exhibit executive monitoring signals but do not possess neurons that control movement initiation.
The paper is impactful because it touches on various topics that are relevant in the contemporary medicine. The treatment of Parkinson’s disease is one of the fields that has been greatly studied, and this makes the paper of great significance. Besides Parkinson’s disease, neurons have also been studied in the experiments, and this helps in imparting knowledge on how neurons work, and due to this, I have a positive attitude that the research will have a positive impact in the field of medicine and psychology as they are the common problems faced in the modern world. The research also has increased my knowledge in regards to the work of the subthalamic nucleus and its relation to Parkinson’s disease as well as have an understanding of the neuron activity and differences.
Reference
Aron, A. R., & Poldrack, R. A. (2006). Cortical and subcortical contributions to stop signal response inhibition: role of the subthalamic nucleus. Journal of Neuroscience, 26(9), 2424-2433.
