Typical visual unfamiliar face individuation in left and right mesial temporal epilepsy

Bidirectional and Cross-Hemispheric Modulations of Face-Selective Neural Activity Induced by Electrical Stimulation within the Human Cortical Face Network

A major scientific objective of cognitive neuroscience is to define cortico-cortical functional connections supporting cognitive functions. Here, we use an original approach combining frequency-tagging and direct electrical stimulation (DES) to test for bidirectional and cross-hemispheric category-specific modulations within the human cortical face network. A unique patient bilaterally implanted with depth electrodes in multiple face-selective cortical regions of the ventral occipito-temporal cortex (VOTC) was shown 70 s sequences of variable natural object images at a 6 Hz rate, objectively identifying deviant face-selective neural activity at 1.2 Hz (i.e., every five images). Concurrent electrical stimulation was separately applied for 10 seconds on four independently defined face-selective sites in the right and left VOTC. Upon stimulation, we observed reduced or even abolished face-selective neural activity locally and, most interestingly, at distant VOTC recording sites. Remote DES effects were found up to the anterior temporal lobe (ATL) in both forward and backward directions along the VOTC, as well as across the two hemispheres. This reduction was specific to face-selective neural activity, with the general 6 Hz visual response being mostly unaffected. Overall, these results shed light on the functional connectivity of the cortical face-selective network, supporting its non-hierarchical organization as well as bidirectional effective category-selective connections between posterior 'core' regions and the ATL. They also pave the way for widespread and systematic development of this approach to better understand the functional and effective connectivity of human brain networks.

The neuropsychological evaluation of face identity recognition

Facial identity recognition (FIR) is arguably the ultimate form of recognition for the adult human brain. Even if the term prosopagnosia is reserved for exceptionally rare brain-damaged cases with a category-specific abrupt loss of FIR at adulthood, subjective and objective impairments or difficulties of FIR are common in the neuropsychological population. Here we provide a critical overview of the evaluation of FIR both for clinicians and researchers in neuropsychology. FIR impairments occur following many causes that should be identified objectively by both general and specific, behavioral and neural examinations. We refute the commonly used dissociation between perceptual and memory deficits/tests for FIR, since even a task involving the discrimination of unfamiliar face images presented side-by-side relies on cortical memories of faces in the right-lateralized ventral occipito-temporal cortex. Another frequently encountered confusion is between specific deficits of the FIR function and a more general impairment of semantic memory (of people), the latter being most often encountered following anterior temporal lobe damage. Many computerized tests aimed at evaluating FIR have appeared over the last two decades, as reviewed here. However, despite undeniable strengths, they often suffer from ecological limitations, difficulties of instruction, as well as a lack of consideration for processing speed and qualitative information. Taking into account these issues, a recently developed behavioral test with natural images manipulating face familiarity, stimulus inversion, and correct response times as a key variable appears promising. The measurement of electroencephalographic (EEG) activity in the frequency domain from fast periodic visual stimulation also appears as a particularly promising tool to complete and enhance the neuropsychological assessment of FIR.

Stability of face recognition abilities after left or right anterior temporal lobectomy

Patients with anterior temporal lobe (ATL) resection due to mesial temporal lobe epilepsy (MTLE) have difficulties at identifying familiar faces and explicitly remembering newly learned faces but their ability to individuate unfamiliar faces remains largely unknown. Moreover, the extent to which their difficulties with familiar face identity recognition and learning is truly due to the ATL resection remains unknown. Here, we report a study of 24 MTLE patients and matched healthy controls tested with an extensive set of seven face and visual object recognition tasks (including three tasks evaluating unfamiliar face individuation) before and about 6 months after unilateral (nine left, 15 right) ATL resection. We found that ATL resection has little or no effect on the patients' preserved pre-surgical ability to perform unfamiliar face individuation, both at the group and individual levels. More surprisingly, ATL resection also has little effect on the patients' performance at recognizing and naming famous faces as well as at learning new faces. A substantial proportion of right MTLE patients (33%) even improved their response times on several tasks, which may indicate a functional release of visuo-spatial processing after resection in the right ATL. Altogether this study shows that face recognition abilities are mainly unaffected by ATL resection in MTLE, either because the critical regions for face recognition are spared or because performance at some tasks is already lower than normal preoperatively. Overall, these findings urge caution when interpreting the causal effect of brain lesions on face recognition ability in patients with ATL resection due to MTLE. They also illustrate the complexity of predicting cognitive outcomes after epilepsy surgery because of the influence of many different intertwined factors.

Comparing neuropsychological functioning in Turkish patients with right and left temporal lobe epilepsy

We compared neuropsychiatric evaluations in temporal lobe epilepsy according to the lateralized hemisphere. Forty-one (68.3%) left-sided temporal lobe epilepsy (LTLE) were compared to 19 right-sided temporal lobe epilepsy (RTLE) (31.7%) (p < 0.001). RTLE mean age was 37 (22-46) years, and LTLE mean age 38 was (30-42). RTLE disease duration was 10 (6-20) years, and LTLE was 22 (10-33) (p < 0.013). Gender (man/woman) for RTLE was 7/12, and for LTLE was 18/23. LTLE scored poorer on the Wechsler Memory Scale (WMS)-III's Mental Control Months-error, WMS-V's "Forward Number Range" and "Backward Number Range" than RTLE (p < 0.017, p < 0.023, p < 0.004). There were differences between hemispheres for "Number of Items Remembered with a Hint" and "Total number of Recalled Items" (WMS-IV) (p < 0.038, p < 0.045). LTLE had lower scores in the Verbal Fluency -K-A-S letters words and WAIS (Wechsler Adult Intelligence Scale) similarity than RTLE (p < 0.019, p < 0.024, p < 0.033, p < 0.026). Oktem and Boston-number of Self-Named Items Tests were poorer in LTLE than RTLE (p < 0.05, p < 0.043). Mental Control Months-error (WMS-III), "Total Number of Recalled Items", "Number of Items Remembered with Hint" (WMS-IV), forward and backward number range (WMS-V), Oktem, Verbal Fluency -K,-A,-S letters words, WAIS similarity, and Boston-number of Self-Named Items tests, can help identify lateralization, particularly in LTLE.

A neural marker of the human face identity familiarity effect

Human adults associate different views of an identity much better for familiar than for unfamiliar faces. However, a robust and consistent neural index of this behavioral face identity familiarity effect (FIFE)-not found in non-human primate species-is lacking. Here we provide such a neural FIFE index, measured implicitly and with one fixation per face. Fourteen participants viewed 70 s stimulation sequences of a large set (n = 40) of widely variable natural images of a face identity at a rate of 6 images/second (6 Hz). Different face identities appeared every 5th image (1.2 Hz). In a sequence, face images were either familiar (i.e., famous) or unfamiliar, participants performing a non-periodic task unrelated to face recognition. The face identity recognition response identified at 1.2 Hz over occipital-temporal regions in the frequency-domain electroencephalogram was 3.4 times larger for familiar than unfamiliar faces. The neural response to familiar faces-which emerged at about 180 ms following face onset-was significant in each individual but a case of prosopdysgnosia. Besides potential clinical and forensic applications to implicitly measure one's knowledge of a face identity, these findings open new perspectives to clarify the neurofunctional source of the FIFE and understand the nature of human face identity recognition.

Revisiting emotion recognition in different types of temporal lobe epilepsy: The influence of facial expression intensity

Temporal lobe epilepsy (TLE) can induce various difficulties in recognizing emotional facial expressions (EFE), particularly for negative valence emotions. However, these difficulties have not been systematically examined according to the localization of the epileptic focus. For this purpose, we used a forced-choice recognition task in which faces expressing fear, sadness, anger, disgust, surprise, or happiness were presented in different intensity levels from moderate to high intensity. The first objective of our study was to evaluate the impact of emotional intensity on the recognition of different categories of EFE in TLE patients compared to control participants. The second objective was to assess the effect of localizationof epileptic focus on the recognition of EFE in patients with medial temporal lobe epilepsy (MTLE) associated or not with hippocampal sclerosis (HS), or lateral temporal lobe epilepsy (LTLE). The results showed that the 272 TLE patients and the 68 control participants were not differently affected by the intensity of EFE. However, we obtained group differences within the clinical population when we took into account the localization of the temporal lobe epileptic focus. As predicted, TLE patients were impaired in recognizing fear and disgust relative to controls. Moreover, the scores of these patients varied according to the localization of the epileptic focus, but not according to the cerebral lateralization of TLE. The facial expression of fear was less well recognized by MTLE patients, with or without HS, and the expression of disgust was less well recognized by LTLE as well as MTLE without HS patients. Moreover, emotional intensity modulated differently the recognition of disgust and surprise of the three patient groups underlying the relevance of using moderate emotional intensity to distinguish the effect of epileptic focus localization. These findings should be taken into account for interpreting the emotional behaviors and deserve to befurther investigated before considering TLE surgical treatment or social cognition interventions in TLE patients.

Intracerebral Electrophysiological Recordings to Understand the Neural Basis of Human Face Recognition

Understanding how the human brain recognizes faces is a primary scientific goal in cognitive neuroscience. Given the limitations of the monkey model of human face recognition, a key approach in this endeavor is the recording of electrophysiological activity with electrodes implanted inside the brain of human epileptic patients. However, this approach faces a number of challenges that must be overcome for meaningful scientific knowledge to emerge. Here we synthesize a 10 year research program combining the recording of intracerebral activity (StereoElectroEncephaloGraphy, SEEG) in the ventral occipito-temporal cortex (VOTC) of large samples of participants and fast periodic visual stimulation (FPVS), to objectively define, quantify, and characterize the neural basis of human face recognition. These large-scale studies reconcile the wide distribution of neural face recognition activity with its (right) hemispheric and regional specialization and extend face-selectivity to anterior regions of the VOTC, including the ventral anterior temporal lobe (VATL) typically affected by magnetic susceptibility artifacts in functional magnetic resonance imaging (fMRI). Clear spatial dissociations in category-selectivity between faces and other meaningful stimuli such as landmarks (houses, medial VOTC regions) or written words (left lateralized VOTC) are found, confirming and extending neuroimaging observations while supporting the validity of the clinical population tested to inform about normal brain function. The recognition of face identity - arguably the ultimate form of recognition for the human brain - beyond mere differences in physical features is essentially supported by selective populations of neurons in the right inferior occipital gyrus and the lateral portion of the middle and anterior fusiform gyrus. In addition, low-frequency and high-frequency broadband iEEG signals of face recognition appear to be largely concordant in the human association cortex. We conclude by outlining the challenges of this research program to understand the neural basis of human face recognition in the next 10 years.

Elucidating the visual phenomena in epilepsy: A mini review

Epilepsy is one of the most recognizable neurological diseases, globally. Epilepsy may be accompanied by various complications, including vision impairments, which may severely impact one's quality of life. These visual phenomena may occur in the preictal, ictal and/or postictal periods of seizures. Examples of epilepsy associated visual phenomena include visual aura, visual hallucinations, transient visual loss and amaurosis (blindness). These ophthalmologic signs/symptoms of epilepsy may be temporary or permanent and may vary depending of the type of epilepsy and location of the seizure foci (occipital or temporal lobe). Some visual phenomena may even be utilized to diagnose the epilepsy type, although solely depending on visual symptoms for diagnosis may lead to mistreatment. Some antiseizure medications (ASMs) may also contribute to certain visual disturbances, thereby impacting its therapeutic efficiency for patients with epilepsy (PWE). Although the development of visual comorbidities has been observed diversely among PWE, there may still be a lack of understanding on their relevance and manifestation in epilepsy, which may contribute to the rate of misdiagnosis and the current scarcity in therapeutic relieve. Therefore, this mini narrative review aimed to discuss the common epilepsy associated visual phenomena, based on the available literature. This review also showcased the relationship between the type of visual complications and the site of seizure onset, as well as compared the visual phenomena between occipital lobe epilepsy and temporal lobe epilepsy. Evaluation of these findings may be crucial in reducing the risk of permanent seizure/epilepsy related vision deficits among PWE.

Face-induced gamma oscillations and event-related potentials in patients with epilepsy: an intracranial EEG study

Background

To examine the pathological effect of a mesial temporal seizure onset zone (SOZ) on local and inter-regional response to faces in the amygdala and other structures of the temporal lobe.

Methods

Intracranial EEG data was obtained from the amygdala, hippocampus, fusiform gyrus and parahippocampal gyrus of nine patients with drug-refractory epilepsy during visual stimulation with faces and mosaics. We analyzed event-related potentials (ERP), gamma frequency power, phase-amplitude coupling and phase-slope-index and compared the results between patients with versus without a mesial temporal SOZ.

Results

In the amygdala and fusiform gyrus, faces triggered higher ERP amplitudes compared to mosaics in both patient groups and higher gamma power in patients without a mesial temporal SOZ. In the hippocampus, famous faces triggered higher gamma power for both groups combined but did not affect ERPs in either group. The differentiated ERP response to famous faces in the parahippocampal gyrus was more pronounced in patients without a mesial temporal SOZ. Phase-amplitude coupling and phase-slope-index results yielded bidirectional modulation between amygdala and fusiform gyrus, and predominately unidirectional modulation between parahippocampal gyrus and hippocampus.

Conclusions

A mesial temporal SOZ was associated with an impaired response to faces in the amygdala, fusiform gyrus and parahippocampal gyrus in our patients. Compared to this, the response to faces in the hippocampus was impaired in patients with, as well as without, a mesial temporal SOZ. Our results support existing evidence for face processing deficits in patients with a mesial temporal SOZ and suggest the pathological effect of a mesial temporal SOZ on the amygdala to play a pivotal role in this matter in particular.

Face processing in the temporal lobe

Face perception is a socially important but complex process with many stages and many facets. There is substantial evidence from many sources that it involves a large extent of the temporal lobe, from the ventral occipitotemporal cortex and superior temporal sulci to anterior temporal regions. While early human neuroimaging work suggested a core face network consisting of the occipital face area, fusiform face area, and posterior superior temporal sulcus, studies in both humans and monkeys show a system of face patches stretching from posterior to anterior in both the superior temporal sulcus and inferotemporal cortex. Sophisticated techniques such as fMRI adaptation have shown that these face-activated regions show responses that have many of the attributes of human face processing. Lesions of some of these regions in humans lead to variants of prosopagnosia, the inability to recognize the identity of a face. Lesion, imaging, and electrophysiologic data all suggest that there is a segregation between identity and expression processing, though some suggest this may be better characterized as a distinction between static and dynamic facial information.

Intracerebral electrical stimulation to understand the neural basis of human face identity recognition

Recognizing people's identity by their faces is a key function in the human species, supported by regions of the ventral occipito-temporal cortex (VOTC). In the last decade, there have been several reports of perceptual face distortion during direct electrical stimulation (DES) with subdural electrodes positioned over a well-known face-selective VOTC region of the right lateral middle fusiform gyrus (LatMidFG; i.e., the "Fusiform Face Area", FFA). However, transient impairments of face identity recognition (FIR) have been extremely rare and only behaviorally quantified during DES with intracerebral (i.e., depth) electrodes in stereo-electroencephalography (SEEG). The three detailed cases reported so far, summarized here, were specifically impaired at FIR during DES inside different anatomical VOTC regions of the right hemisphere: the inferior occipital gyrus (IOG) and the LatMidFG, as well as a region that lies at the heart of a large magnetic susceptibility artifact in functional magnetic resonance imaging (fMRI): the anterior fusiform gyrus (AntFG). In the first two regions, the eloquent electrode contacts were systematically associated with the highest face-selective and (unfamiliar) face individuation responses as measured with intracerebral electrophysiology. Stimulation in the right AntFG did not lead to perceptual changes but also caused an inability to remember having been presented face pictures, as if the episode was never recorded in memory. These observations support the view of an extensive network of face-selective VOTC regions subtending human FIR, with at least three critical nodes in the right hemisphere associated with differential intrinsic and extrinsic patterns of reentrant connectivity.