Target
Bilateral Cingulotomy targets the anterior cingulate cortex, which is a part of the limbic system. This system is responsible for the integration of feelings and emotion in the human cortex. It consists of the cingulate gyrus, parahippocampal gyrus and the hippocampal formation.
Studies in patients that were a subject to bilateral cingulotomy, that involved fMRI analyses, showed that the anterior cingulate cortex has a key role in cognitive control and is highly likely to be involved in the control of attentional response, whereas the dorsal part of that region of the brain was not identified to be involved in such a process, although this is still under dispute. The function of the dorsal part of the cingulate cortex was connected to the sorting out and processing of conflicting information signals. In addition, neuroimaging studies also indicated that the anterior cingulate cortex participates in the modulation of cortical regions that are of higher order as well as sensory processing areas.
These findings have also been confirmed by stereotactic microelectrode analysis of single cortical neurons in a study, which involved nine patients undergoing bilateral cingulotomy. The study investigated the effect of performing attention demanding tasks on the activity of 36 neurons located in the anterior cingulate cortex. Upon analyzing of the results of the study it was concluded that the anterior cingulate cortex is indeed involved in the modification of cognitive tasks that require attention based on the fact that there was a change in the basal firing rate of neurons in that region during simulation of such tasks.
Neuroimaging also uncovered different sub-regions in the anterior cingulate cortex itself based on their function. It was proven that the caudal part of the anterior cingulate cortex plays a more important function in cognitive activities that involve attention, salience, interference and response competition. These results combined with electrophysiological investigation of the function of neurons in the anterior cingulate cortex have provided insights that can be used in the improvement of cingulotomy performed on patients treated for OCD. The basis behind this idea is the fact that a variation of certain tasks, Emotional Stroop tasks (ES), which have been particularly identified as exerting effects in OCD patients activate neurons in the more rostral part of the anterior cingulate cortex. Thus, theoretically if bilateral cingulotomy is performed in such patient in the rostral anterior cingulate cortex, better results should be obtained.
Moreover, OCD has been associated with a malformation of the basal ganglia . The function of this part of the human brain has been mapped to be composed of fiber tracks associated with numerous parallel cortico-striato-thalamocortical circuits (CSTC), which are involved in sensorimotor, motor, oculomotor as well as the cognitive processes that are manifested by the limbic system. This pathway involves GABAergic inhibitory projections that serve as one of the means of communication between the different structures involved. It has been hypothesized that some forms of OCD are a result of disinhibition of a one or several of the circuits that operate in the CSTC. This is also indicated by a finding that showed a significant decrease in intracortical inhibition in OCD patients. Thus, lesions in the anterior cingulate cortex might contribute to the lessening of the disinhibition effect. This theory has been confirmed by another study which assessed the cortical inhibitory and excitatory mechanisms in OCD. The study measured the excitability of motor cortex, as well as intracortical inhibition in OCD patients and a control of healthy individuals. The results showed a significant decrease in intracortical inhibition, which resulted in a slowdown of interstimulus intervals by 3msec. In addition to its proximity to and association with the limbic system and the amygdala in particular, which plays a key role in emotional experience, the anterior cingulate cortex shares afferent and efferent pathways with a number of thalamic nuclei as well as the posterior cingulate and part of some parietal, frontal and supplementary motor cortex. All these underline the high likelihood that the anterior cingulate cortex must be linked to OCD.
Functional MRI analyses of the anterior cingulate cortex have also led to the introduction of bilateral cingulotomy for the treatment of chronic pain. Such application was introduced since the anterior cingulate cortex has been found to be related to the processing nociceptive information input. In particular the role of the anterior cingulate cortex is in the interpretation of how a stimulus affects a person rather than its actual physical intensity.
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