Mapping of the Somatosensory Cortex

Abstract

Intraoperative sensory cortical mapping is a reliable and safe method for the functional localization of the central sulcus (CS). It is utilized during neurosurgical procedures performed near eloquent brain tissue. It helps in identifying the somatosensory cortex and CS, hence preventing any postoperative neurological deficits. When executed properly, this method can identify the somatosensory cortex for both the upper and lower limbs by locating the CS. This technical report outlines the benefits of cortical sensory mapping (CsM) and detailed methodology. With the help of a properly trained intraoperative neuromonitoring staff who can accurately interpret the signals being monitored, CsM can help in injury prevention during brain surgeries.

Unsupervised machine learning can delineate central sulcus by using the spatiotemporal characteristic of somatosensory evoked potentials

“…However, when the interelectrode distance becomes too large, it is easily influenced by electrocardiogram and muscle artifacts, which increases the complexity of the ECoG analysis [ 4 , 25 , 28 ]. These difficulties lead to multiple strip placements on the craniotomy [ 21 , 24 , 25 , 32 ]. Furthermore, the routine clinical MSSEP-PRT relies only on the amplitude construal of the conventional N20 (posterior) and P20 (anterior) between the two adjacent contacts to delineate the CS.…”

“…This may be due to cortical displacements, caused by either the tumor invasion or peritumoral edema [ 4 ]. It may also be due to the placement of strip electrode away from the localized nature of the hand area [ 24 , 33 ]. Several investigators have described how several recordings with the use of a single strip in different locations might be needed to find the appropriate position to target the somatosensory cortex [ 13 , 25 , 29 , 31 , 33 , 53 ], whose success needs to be further corroborated by DCS [ 4 , 24 , 35 ] when there is persistent doubt.…”

“…It may also be due to the placement of strip electrode away from the localized nature of the hand area [ 24 , 33 ]. Several investigators have described how several recordings with the use of a single strip in different locations might be needed to find the appropriate position to target the somatosensory cortex [ 13 , 25 , 29 , 31 , 33 , 53 ], whose success needs to be further corroborated by DCS [ 4 , 24 , 35 ] when there is persistent doubt. The multiple electrode relocation and placements require significant time and the additional risk of hemorrhage and trauma, while DCS requires a rigorous anesthetic regimen [ 39 ] and may induce seizures that could jeopardize the surgical procedure or complicate the motor monitorization.…”

“…These peaks exhibited a lateral orientation to the hand knob in figure 4 , which was first seen by Wood et al [ 29 ], for the 1st N/N20 peak. Wood et al showed that due to the bend on of the CS in the hand area, which commonly forms a convex cap of tissue pointing toward the frontal midline, there exists an ‘on-axis’ line passing through the maxima of the N20 and P30, forming an acute 70° line nearing the overall course of the CS [ 13 , 24 , 29 ].…”

Mapping of the Language Cortex

“…Contralateral median nerve stimulation is used to generate phase reversal at the central sulcus (Figure 1 ). Recording filters are set at 30-3000 Hz with a time base of 100 milliseconds [ 5 ]. The CS and somatosensory cortex are localized by generating multiple sensory maps by stimulating the contralateral median nerve at a current of 20-35 mA between frequencies of 2.66-4.79 Hz.…”