Intraoperative functional mapping of calculation in parietal surgery. New insights and clinical implications.

BACKGROUND: Parietal areas play a crucial role in calculation processing. The purpose of this study is to report our experience in the assessment of calculation processing during awake surgery in parietal areas, focusing on clinical implications and new insights provided by this approach. METHODS: We retrospectively reviewed clinical and surgical data of 13 patients who underwent parietal surgery with calculation mapping. Cortical and sub-cortical areas (in 13 and five patients, respectively) involved in single-digit multiplications and additions were identified using bipolar electro-stimulation. RESULTS: Cortical stimulation data showed that the inferior parietal lobule and the intraparietal sulcus were specifically related to calculation in all cases, regardless of the side (100% of cases, in both sides). Conversely, the superior parietal lobule was inconstantly involved in calculation processing (40% of cases in the left and 75% in the right side), whereas the somatosensory area was never involved. Sub-cortical stimulation was able to detect functional areas for calculation in all patients: in 90% of cases the sub-cortical sites positive for calculation were in close anatomical connection with the cortical sites mapping for the same function. The intraoperative preservation (-or damaging-) of functional sites correlated with the absence (- or occurrence-) of post-operative calculation processing impairment. CONCLUSIONS: Our findings support the specificity of the reported technique in the intraoperative identification of sites functional for calculation. Our data show the bilateral involvement of parietal cortex, especially of the inferior lobule, in calculation processing. Furthermore, our study suggests the existence of a sub-cortical pathway specific for calculation, whose better understanding might be crucial for the clinical outcome of patients.

Functional mapping of left parietal areas involved in simple addition and multiplication. A single-case study of qualitative analysis of errors.

All electrostimulation studies on arithmetic have so far solely reported general errors. Nonetheless, a classification of the errors during stimulation can inform us about underlying arithmetic processes. The present electrostimulation study was performed in a case of left parietal glioma. The patient's erroneous responses suggested that calculation was mainly applied for addition and a combination of retrieval and calculation was mainly applied for multiplication. The findings of the present single-case study encourage follow up with further data collection with the same paradigm.

Top-down regulation of left temporal cortex by hypnotic amusia for rhythm: a pilot study on mismatch negativity.

To evaluate the effect of hypnotically induced amusia for rhythm (a condition in which individuals are unable to recognize melodies or rhythms) on mismatch negativity (MMN), 5 highly (HH) and 5 poorly (LH) hypnotizable nonmusician volunteers underwent MMN recording before and during a hypnotic suggestion for amusia. MMN amplitude was recorded using a 19-channel montage and then processed using the low-resolution electromagnetic tomography (LORETA) to localize its sources. MMN amplitude was significantly decreased during hypnotic amusia (p < .04) only in HH, where the LORETA maps of MMN showed a decreased source amplitude in the left temporal lobe, suggesting a hypnotic top-down regulation of activity of these areas and that these changes can be assessed by neurophysiological investigations.

Right parietal cortex and calculation processing: intraoperative functional mapping of multiplication and addition in patients affected by a brain tumor.

OBJECT: The role of parietal areas in number processing is well known. The significance of intraoperative functional mapping of these areas has been only partially explored, however, and only a few discordant data are available in the surgical literature with regard to the right parietal lobe. The purpose of this study was to evaluate the clinical impact of simple calculation in cortical electrostimulation of right-handed patients affected by a right parietal brain tumor. METHODS: Calculation mapping in awake surgery was performed in 3 right-handed patients affected by high-grade gliomas located in the right parietal lobe. Preoperatively, none of the patients presented with calculation deficits. In all 3 cases, after sensorimotor and language mapping, cortical and intraparietal sulcus areas involved in single-digit multiplication and addition calculations were mapped using bipolar electrostimulation. RESULTS: In all patients, different sites of the right parietal cortex, mainly in the inferior lobule, were detected as being specifically related to calculation (multiplication or addition). In 2 patients the intraparietal sulcus was functionally specific for multiplication. No functional sites for language were detected. All sites functional for calculation were spared during tumor resection, which was complete in all cases without postoperative neurological deficits. CONCLUSIONS: These findings provide intraoperative data in support of an anatomofunctional organization for multiplication and addition within the right parietal area. Furthermore, the study shows the potential clinical relevance of intraoperative mapping of calculation in patients undergoing surgery in the right parietal area. Further and larger studies are needed to confirm these data and assess whether mapped areas are effectively essential for function.