The contribution of right frontal regions to cognition is relatively poorly understood compared to language, praxis and executive functions of homologous regions in the left hemisphere. Indeed, when it comes to tumour resection, it is often assumed that right frontal regions make little appreciable contribution to cognitive function. As a result, intraoperative mapping of ‘functionally eloquent’ regions is often confined to cases where the tumour is in the language-dominant left hemisphere or near motor regions.
Puglisi et al (2019) investigated whether right frontal regions might play a causal role in executive function by assessing performance on the Stroop task. The authors stimulated cortical regions and subcortical white matter while awake patients performed the test, which measures the ability of people to inhibit their prepotent tendency to read a word instead of giving its font colour.
Stimulation of a region of white matter just deep to the right inferior frontal gyrus led to errors on the Stroop task, most likely due to disruption of inferior fronto-striatal tracts linking cortical areas to basal ganglia regions. Further, lesion mapping revealed that resection of the inferior frontal gyrus was associated with slower performance on the Stroop task.
The results of this study show how intraoperative mapping can contribute both to improving scientific understanding of right frontal lobe function and in surgical planning of tumour resection. It is intriguing in this context that another recent investigation reports that cognitive outcomes are significantly worse after right hemisphere glioma surgery compared to left (Hendriks et al. 2018).
Key points:
- Right frontal regions have been considered to be functionally ‘ineloquent’ so surgery for tumours in this region rarely involves mapping with intraoperative electrical stimulation.
- This study using intraoperative mapping in awake patients shows that right inferior frontal regions play a key role in inhibitory control.
- The crucial stimulation site was in the right inferior fronto-striatal white matter pathway connecting frontal cortical regions to the basal ganglia.
- This may be important in the context of new data which show that cognitive decline is more profound after right hemisphere resection of gliomas.
References:
Hendriks EJ, Habets EJJ, Taphoorn MJB, Douw L, Zwinderman AH, Vandertop WP, Barkhof F, Klein M, De Witt Hamer PC (2018) Linking late cognitive outcome with glioma surgery location using resection cavity maps. Hum Brain Mapp. 39:2064-2074.