Functional differences among stimulation-identified cortical naming sites in the temporal region

Abstract

To preserve postoperative language, electrical stimulation mapping is often conducted prior to surgery involving the language dominant hemisphere. Object naming is the task most widely used to identify language cortex, and sites where stimulation elicits naming difficulty are typically spared from resection. In clinical practice, sites classified as positive undergo no further testing regarding the underlying cause of naming failure. Word production is a complex function involving multiple mechanisms that culminate in the identification of the target word. Two main mechanisms, i.e., semantic and phonological, underlie the retrieval of stored information regarding word meaning and word sounds, and naming can be hampered by disrupting either of these. These two mechanisms are likely mediated by different brain areas, and therefore, stimulation-identified naming sites might not be functionally equivalent. We investigated whether further testing at stimulation-identified naming sites would reveal an anatomical dissociation between these two mechanisms. In 16 refractory temporal lobe epilepsy (TLE) patients with implanted subdural electrodes, we tested whether, despite inability to produce an item name, patients could reliably access semantic or phonological information regarding objects during cortical stimulation. We found that stimulation at naming sites in superior temporal cortex tended to impair phonological processing, yet spared access to semantic information. By contrast, stimulation of inferior temporal naming sites revealed a greater proportion of sites where semantic access was impaired, and a dissociation between sites where stimulation spared or disrupted semantic or phonological processing. These functional-anatomical dissociations reveal the more specific contribution to naming provided by these cortical areas and shed light on the often profound, interictal word-finding deficit observed in temporal lobe epilepsy. Additionally, these techniques potentially lay the groundwork for future studies to determine whether particular naming sites that fall within the margins of the desired clinical resection might be resected without significant risk of decline.

Impaired naming performance in temporal lobe epilepsy: language fMRI responses are modulated by disease characteristics

“…Overall, this is consistent with the notion that auditory naming tasks are associated with increased semantic/executive control as well as working memory demands [ 21 ]. In accord with previous experiments [ 22 , 23 ], auditory naming led to activations in both anterior and posterior temporal regions, while picture naming only activated the posterior part of the fusiform gyrus. We recently performed a longitudinal analysis in 46 TLE patients undergoing ATLR, comprising a subgroup of 35 patients of the cohort of this study, in which we demonstrated that posterior inferior temporal and posterior fusiform fMRI activation during auditory, respectively, picture naming can be used to predict naming decline after ATLR with very high specificity at maximum sensitivity [ 24 ].…”

Topographical gradients of semantics and phonology revealed by temporal lobe stimulation

“…However, while their analyses revealed clustering of semantic errors at the junction of posterior STG and supramarginal gyrus, in our corpus semantic errors tended to occur more inferiorly, a discrepancy possibly reflecting the smaller error sample analyzed by Tate et al []. Interestingly, these results converged with those from Hamberger et al [] who probed the information available to patients during left temporal stimulation despite naming failure. Patients were queried about semantic features ( Is it found indoors? )…”

“…Accordingly, word retrieval has traditionally been conceived as involving two broad selection processes: one concerning word meaning (i.e., semantic processing), and the other related to information about word sounds that functions as input to articulation (i.e, phonological processing). Direct cortical stimulation can give rise to specific and differentiated naming errors [Corina, et al, ; Hamberger, ; Hamberger et al, ; Ojemann et al, ; Tate et al, ] resembling errors that are produced naturally by neurologically intact speakers or individuals suffering from neuropathologies that impair language (e.g., aphasia). To the extent that cortical stimulation induces language dysfunction at an extremely localized neural level, naming errors elicited by stimulation in temporal cortices provide a unique opportunity to shed a more detailed light on the neurofunctional organization of word production in this region.…”

Cognitive and Emotional Mapping With SEEG

“…Regions spanning the ventral temporal and occipital lobes and fusiform area appear to contribute heavily to recognition (primarily right hemisphere, but some left) of visual objects and faces, while coexisting areas on the left are important for naming (152)(153)(154)(155)(156). Naming itself is a complex (161)]. The latter tasks require the subject to determine the semantic content before applying the name, and are therefore slightly more complex.…”