Neurobioetica: La Persona al centro
delle Neuroscienze, Etica, Diritto e Società
Roma, 2 luglio 2012
Modulo 1 : Fondamenti ed Etica delle Neuroscienze
Continuo, questo post, l’approfondimento neuroscientifico relativo alla recente pubblicazione intitolata: Direct electrical stimulation (DES) of human cortex — the gold standard for mapping brain functions? uscita lo scorso gennaio 2012 sulla prestigiosa rivista Nature Reviews Neuroscience (vol. 13, 63-70). Svenja Borchers et al. utilizzando la stimolazione elettrica corticale, tentarono di “mappare” diverse funzioni cerebrali superiori.
Questo è un tipico esempio di approccio bottom-up che dalla stimolazione di aree cerebrali osserva i cambiamenti comportamentali corrispondenti.
DES (Direct electrical stimulation of human cortex) as a clinical tool
Intraoperative DES in patients with brain tumours or with intractable epilepsy aids surgery by identifying brain areas that are critical for important functions4, 7, 8, 13, 14, 15. The ability to map critical locations for each individual has tremendous clinical value, as the location of brain function varies between patients owing to normal individual variability of cortical organization and to functional reorganization in response to the individual's brain pathology. Evaluation of postoperative performance following resection of brain tissue has proven the reliability of intrasurgical DES in mapping cortical functions.
For example, a very low rate (less than 2% of 250 patients) of postsurgical permanent language deficits was observed when intraoperative DES was used to map language functions8. Conversely, partial resection of language sites that had been detected by DES prevented complete recovery of language functions16. DES can also be used to directly study both anatomical and functional connectivity at the same time. For example, it has been shown that intraoperative DES mapping of subcortical structures can avoid damage to the connecting fibres of the semantic language system, thus preventing permanent language deficits7. When intraoperative DES was used for functional mapping of the motor system, 87% of 55 investigated patients showed no postoperative motor deficits 1 month after resection of tumours located near the corticospinal tract17. Spena et al. investigated whether functional MRI (fMRI) and diffusion tensor imaging (DTI) fibre tracking is as useful as DES in predicting tissue function in 'eloquent regions' before tumour resection18. They found DES to be the most reliable method for preventing persistent neurological impairments and concluded that fMRI and DTI might be useful for planning the resection but cannot be used to directly lead the surgeon during the operation.
Although the objective of DES in a clinical context is straightforward — preventing a loss of function after resection — the use of DES in a neuroscience context raises several questions with respect to its neurophysiological effects.
Does DES evoke neuronal activation or inhibition?
Does DES induce current spread, and is there inter-regional signal propagation? What is the role of cortico–thalamo–cortical pathways in positive or negative behavioural effects of DES?
In order to use DES results for developing neurocognitive models of brain function, it is essential to understand the cellular, local and remote effects of this method.