The role of the temporal poles in proper naming and people recognition: a tDCS study

Even if extensively studied, the neural correlates of people’s recognition and naming are still a matter of debate. While neuropsychological reports on single cases show a greater role of the left anterior temporal lobe (ATL) in proper naming and of the right one in people’s identification, reviews are less consistent (Gainotti et al., 2007). Moreover, it is still controversial whether the familiarity feeling, personal semantics access and proper names retrieval depend on amodal processes, relying on supra-modal hubs, or follows modality-dependent paths (Gainotti et al., 2007; Patterson et al., 2007; Ralph and Patterson, 2008). To disentangle these issues, we tested, in a parallel group design, healthy subjects performance in famous people recognition and naming after anodal tDCS, over the left or right ATL or after a placebo stimulation condition. tDCS a non-invasive brain stimulation technique, which is supposed to enhance spontaneous cortical activity when delivered with the anodal polarity. In the famous people recognition task, subjects were presented with visual (face recognition) or auditory (voice recognition) stimuli, belonging either to famous or non-famous persons. Participants had first to indicate whether it was a famous person (familiarity test); then, if the stimulus was recognized as famous, participants had to provide some personal semantic information; finally, subjects had to produce the name of the famous person. We expected left anodal tDCS to affect performance in proper naming only and, in turn, right ATL simulation to modulate familiarity and personal semantics access. Data on 16 participants for both right ATL and sham tDCS groups are available, while six subjects have been collected up to now for left ATL tDCS. Concerning famous faces recognition, mixed effects models confirmed that familiarity resulted affected by stimulation (Stimulation*Celebrity: χ2(2)=20.0739; p<.001), with right tDCS boosting the recognition of non-famous faces as compared to sham stimulation (98.5% vs 91.1%; p=.001). RTs for non-famous faces were faster in the right compared to sham tDCS (F(2,1387)=4.15; p=.016; right-tDCS:1716 ms; sham-tDCS:2122ms; p=.004). This result is in line with neuropsychological findings reporting right ATL lesioned patients having problems with recognizing as non-famous unknown people. Similarly, personal semantics resulted enhanced after right anodal ATL tDCS (χ2(2)=5.8; p=.05). This group was more accurate (96.6%) in retrieving information about famous persons as compared to the sham (93.6; p=.04) and marginally to the left tDCS (92.4%; p=.056) groups. Finally, proper naming was boosted by left ATL tDCS (χ2(2)= 7.5; p=.02), being this group better (95.2%) with respect to both the right (81.1%; p=.009) and the sham (80.8; p=.008) tDCS groups. No significant effect of tDCS has been highlighted for famous voices recognition. Our data support a key role of the right ATL in famous people recognition and access to personal semantics, while the left ATL seems crucial for proper naming.