Neural processing of high and low spatial frequency information in faces changes across development: qualitative changes in face processing during adolescence

Face perception in adults depends on skilled processing of interattribute distances (‘configural’ processing), which is disrupted for faces presented in inverted orientation (face inversion effect or FIE). Children are not proficient in configural processing, and this might relate to an underlying immaturity to use facial information in low spatial frequency (SF) ranges, which capture the coarse information needed for configural processing. We hypothesized that during adolescence a shift from use of high to low SF information takes place. Therefore, we studied the influence of SF content on neural face processing in groups of children (9–10 years), adolescents (14–15 years) and young adults (21–29 years) by measuring event‐related potentials (ERPs) to upright and inverted faces which varied in SF content. Results revealed that children show a neural FIE in early processing stages (i.e. P1; generated in early visual areas), suggesting a superficial, global facial analysis. In contrast, ERPs of adults revealed an FIE at later processing stages (i.e. N170; generated in face‐selective, higher visual areas). Interestingly, adolescents showed FIEs in both processing stages, suggesting a hybrid developmental stage. Furthermore, adolescents and adults showed FIEs for stimuli containing low SF information, whereas such effects were driven by both low and high SF information in children. These results indicate that face processing has a protracted maturational course into adolescence, and is dependent on changes in SF processing. During adolescence, sensitivity to configural cues is developed, which aids the fast and holistic processing that is so special for faces.     

Cortical oscillations and entrainment in speech processing during working memory load

Neuronal oscillations are thought to play an important role in working memory (WM) and speech processing. Listening to speech in real‐life situations is often cognitively demanding but it is unknown whether WM load influences how auditory cortical activity synchronizes to speech features. Here, we developed an auditory n‐back paradigm to investigate cortical entrainment to speech envelope fluctuations under different degrees of WM load. We measured the electroencephalogram, pupil dilations and behavioural performance from 22 subjects listening to continuous speech with an embedded n‐back task. The speech stimuli consisted of long spoken number sequences created to match natural speech in terms of sentence intonation, syllabic rate and phonetic content. To burden different WM functions during speech processing, listeners performed an n‐back task on the speech sequences in different levels of background noise. Increasing WM load at higher n‐back levels was associated with a decrease in posterior alpha power as well as increased pupil dilations. Frontal theta power increased at the start of the trial and increased additionally with higher n‐back level. The observed alpha–theta power changes are consistent with visual n‐back paradigms suggesting general oscillatory correlates of WM processing load. Speech entrainment was measured as a linear mapping between the envelope of the speech signal and low‐frequency cortical activity (< 13 Hz). We found that increases in both types of WM load (background noise and n‐back level) decreased cortical speech envelope entrainment. Although entrainment persisted under high load, our results suggest a top‐down influence of WM processing on cortical speech entrainment.     

Alpha activity marking word boundaries mediates speech segmentation

This study examined the neurophysiological mechanisms of speech segmentation, the process of parsing the continuous speech signal into isolated words. Individuals listened to sequences of two monosyllabic words (e.g. gas source) and non‐words (e.g. nas sorf). When these phrases are spoken, talkers usually produce one continuous s‐sound, not two distinct s‐sounds, making it unclear where one word ends and the next one begins. This ambiguity in the signal can also result in perceptual ambiguity, causing the sequence to be heard as one word (failed to segment) or two words (segmented). We compared listeners' electroencephalogram activity when they reported hearing one word or two words, and found that bursts of fronto‐central alpha activity (9–14 Hz), following the onset of the physical /s/ and end of phrase, indexed speech segmentation. Left‐lateralized beta activity (14–18 Hz) following the end of phrase distinguished word from non‐word segmentation. A hallmark of enhanced alpha activity is that it reflects inhibition of task‐irrelevant neural populations. Thus, the current results suggest that disengagement of neural processes that become irrelevant as the words unfold marks word boundaries in continuous speech, leading to segmentation. Beta activity is likely associated with unifying word representations into coherent phrases.     

Interaction of synchronized dynamics in cortex and basal ganglia in Parkinson's disease

Parkinson's disease pathophysiology is marked by increased oscillatory and synchronous activity in the beta frequency band in cortical and basal ganglia circuits. This study explores the functional connections between synchronized dynamics of cortical areas and synchronized dynamics of subcortical areas in Parkinson's disease. We simultaneously recorded neuronal units (spikes) and local field potentials (LFP) from subthalamic nucleus (STN) and electroencephalograms (EEGs) from the scalp in parkinsonian patients, and analysed the correlation between the time courses of the spike–LFP synchronization and inter‐electrode EEG synchronization. We found the (non‐invasively obtained) time course of the synchrony strength between EEG electrodes and the (invasively obtained) time course of the synchrony between spiking units and LFP in STN to be weakly, but significantly, correlated with each other. This correlation is largest for the bilateral motor EEG synchronization, followed by bilateral frontal EEG synchronization. Our observations suggest that there may be multiple functional modes by which the cortical and basal ganglia circuits interact with each other in Parkinson's disease: not only may synchronization be observed between some areas in cortex and the basal ganglia, but also synchronization within cortex and within basal ganglia may be related, suggesting potentially a more global functional interaction. More coherent dynamics in one brain region may modulate or activate the dynamics of another brain region in a more powerful way, causing correlations between changes in synchrony strength in the two regions.     

Neural correlates of endogenous attention,exogenous attention and inhibition of return in touch

Selective attention helps process the myriad of information constantly touching our body. Both endogenous and exogenous mechanisms are relied upon to effectively process this information; however, it is unclear how they relate in the sense of touch. In three tasks we contrasted endogenous and exogenous event‐related potential (ERP) and behavioural effects. Unilateral tactile cues were followed by a tactile target at the same or opposite hand. Clear behavioural effects showed facilitation of expected targets both when the cue predicted targets at the same (endogenous predictive task) and opposite hand (endogenous counter‐predictive task), and these effects also correlated with ERP effects of endogenous attention. In an exogenous task, where the cue was non‐informative, inhibition of return (IOR) was observed. The electrophysiological results demonstrated early effects of exogenous attention followed by later endogenous attention modulations. These effects were independent in both the endogenous predictive and exogenous tasks. However, voluntarily directing attention away from a cued body part influenced the early exogenous marker (N80). This suggests that the two mechanisms are interdependent, at least when the task requires more demanding shifts of attention. The early marker of exogenous tactile attention, the N80, was not directly related to IOR, which may suggest that exogenous attention and IOR are not necessarily two sides of the same coin. This study adds valuable new insight into how we process and select information presented to our body, showing both independent and interdependent effects of endogenous and exogenous attention in touch.     

Diagnostic test utilization in evaluation for resective epilepsy surgery in children

Epilepsy surgery is highly successful in achieving seizure freedom in carefully selected children with drug‐resistant focal epilepsy. Advances in technology have aided presurgical evaluation and increased the number of possible candidates. Many of the tests employed are resource intense, and in specific cases they may be unhelpful or have adverse effects. Some standardization of the evaluation process is thus considered timely. Given the lack of class 1 or 2 evidence defining the relative utility of each test in specific clinicopathologic cohorts, a set of expert recommendations was attempted using consensus among members of the Pediatric Epilepsy Surgery Task Force of the International League Against Epilepsy (ILAE) Commissions of Pediatrics and Diagnostics These recommendations aim to limit fringe over or underutilization of use while retaining substantial flexibility in the use of various tests, in keeping with most standard practices at established pediatric epilepsy centers. A PowerPoint slide summarizing this article is available for download in the Supporting Information section here .     

Distress‐dependent temporal variability of regions encoding domain‐specific and domain‐general behavioral manifestations of phantom percepts

Tinnitus is the perception of a phantom sound characterized behaviorally by a loudness and a distress component. Although a wealth of information is available about the relationship between these behavioral correlates and changes in static functional connectivity, its relationship with dynamic changes in network connectivity is yet unexplored. The aim of this study was thus to investigate changes in the flexibility and stability of temporal variability in tinnitus and its relation to loudness and distress using continuous resting‐state EEG. We observe an increase in temporal variability at the whole‐brain level in tinnitus, which is spatiotemporally distributed at the nodal level. Behaviorally, we observe changes in the relationship between temporal variability and loudness and distress depending on the amount of distress experienced. In patients with low distress, there is no relationship between temporal variability and loudness or distress, demonstrating a resilience in dynamic connectivity of the brain. However, patients with high distress exhibit a direct relationship with increasing loudness in the primary auditory cortex and parahippocampus, and an inverse relationship with increasing distress in the parahippocampus. In tinnitus, the specific sensory (loudness) component related to increased temporal variability possibly reflects a Bayesian search for updating deafferentation‐based missing information. On the other hand, the decreased temporal variability related to the nonspecific distress component possibly reflects a more hard‐wired or less adaptive contextual processing. Therefore, our findings may reveal a way to understand the changes in network dynamics not just in tinnitus, but also in other brain disorders.     

Reduced late mismatch negativity and auditory sustained potential to rule‐based patterns in schizophrenia

Complex rule‐based auditory processing is abnormal in individuals with long‐term schizophrenia (SZ), as demonstrated by reduced mismatch negativity (MMN) to deviants in rule‐based patterns and reduced auditory sustained potential (ASP) that appears when grouping tones together. Together, this suggests deficits later in the auditory processing hierarchy in Sz. Here, MMN and ASP were elicited by deviations from a complex zig‐zag pitch pattern that cannot be predicted by simple linear rules. Twenty‐seven SZ and 26 matched healthy controls (HC) participated. Frequent groups of patterns contained eight tones that zig‐zagged in a two‐up one‐down pitch‐based paradigm. There were two deviant patterns: the final tone was either higher in pitch than expected (creating a jump in pitch) or was repeated. Simple MMN to pitch‐deviants among repetitive tones was measured for comparison. Sz exhibited a smaller pitch MMN compared to HC as expected. HC produced a late MMN in response to the repeat and jump‐deviant and a larger ASP to the standard group of tones, all of which were significantly blunted in SZ. In Sz, the amplitude of the late complex MMN was related to neuropsychological functioning, whereas ASP was not. ASP and late MMN did not significantly correlate in HC or in Sz, suggesting that they are not dependent on one another and may originate within distinct processing streams. Together, this suggests multiple deficits later in the auditory sensory‐perceptual hierarchy in Sz, with impairments evident in both segmentation and deviance detection abilities.     

The spatio‐temporal profile of multisensory integration

Task‐irrelevant visual stimuli can enhance auditory perception. However, while there is some neurophysiological evidence for mechanisms that underlie the phenomenon, the neural basis of visually induced effects on auditory perception remains unknown. Combining fMRI and EEG with psychophysical measurements in two independent studies, we identified the neural underpinnings and temporal dynamics of visually induced auditory enhancement. Lower‐ and higher‐intensity sounds were paired with a non‐informative visual stimulus, while participants performed an auditory detection task. Behaviourally, visual co‐stimulation enhanced auditory sensitivity. Using fMRI, enhanced BOLD signals were observed in primary auditory cortex for low‐intensity audiovisual stimuli which scaled with subject‐specific enhancement in perceptual sensitivity. Concordantly, a modulation of event‐related potentials could already be observed over frontal electrodes at an early latency (30–80 ms), which again scaled with subject‐specific behavioural benefits. Later modulations starting around 280 ms, that is in the time range of the P3, did not fit this pattern of brain‐behaviour correspondence. Hence, the latency of the corresponding fMRI‐EEG brain‐behaviour modulation points at an early interplay of visual and auditory signals in low‐level auditory cortex, potentially mediated by crosstalk at the level of the thalamus. However, fMRI signals in primary auditory cortex, auditory thalamus and the P50 for higher‐intensity auditory stimuli were also elevated by visual co‐stimulation (in the absence of any behavioural effect) suggesting a general, intensity‐independent integration mechanism. We propose that this automatic interaction occurs at the level of the thalamus and might signify a first step of audiovisual interplay necessary for visually induced perceptual enhancement of auditory perception.     

Cross‐sensory modulation of alpha oscillatory activity: suppression,idling, and default resource allocation

Alpha oscillations (~10 Hz) have been suggested to have an inhibitory influence on stimulus processing within the context of attention being coordinated across space, with an increase in the power of alpha activity occurring in spatially irrelevant regions. However, with respect to cross‐sensory attention (distribution of attention to different sensory modalities) an increase in alpha activity from baseline has not yet been definitively linked to active inhibition of distraction. In the current study, we examined the role of top‐down alpha modulation in facilitating and suppressing stimulus processing between the visual and auditory domain. We utilized two cross‐sensory paradigms, one containing distractors while the other paradigm only contained targets, in order to separate distractor related activity. We found a cue induced increase from baseline for the power of occipital alpha activity in posterior cortex when participants anticipated the occurrence of auditory targets combined with visual distractors. Interestingly, there was no increase in alpha power observed in the condition where auditory targets occurred without distractors. These findings suggest that the increase in alpha activity from baseline reflects top‐down drive processes serving to inhibit distracting input. However, we found that there was no significant difference in the absolute occipital alpha power between when participants were expecting a visual distractor, and the session where no visual distractors were present. We account for these findings by suggesting that an increase in alpha power in the anticipation of visual distractors, rather than being exclusively inhibitory, could also signal the re‐allocation of resources in the sensory systems.     

An electrophysiological marker of the desire to quit in smokers

For many smokers, the motivational state of craving is a central feature of their dependence on nicotine, and is often at odds with a general desire to quit. How this desire to quit may influence the craving for a cigarette, however, is unclear. In the current study, we manipulated the level of craving in 24 regular smokers, and recorded EEG measures of brain activity during a rare target detection task utilizing addiction‐unrelated stimuli. In response to the non‐targets, we observed that smokers wanting to quit showed an enhanced late frontal activation when they were craving vs. not craving, whereas smokers not wanting to quit showed the opposite pattern of activity. A dissociation was also present in the target‐related P300 response as a function of craving and desire to quit, with smokers who did not want to quit processing targets differentially between the states of craving and non‐craving. The data suggest that distinct top‐down control mechanisms during craving may be implemented by people who wish to quit smoking, as compared to those who do not wish to quit. This pattern of findings establishes this ERP activity as a potential biomarker that may help to differentiate people who want to quit their addiction from those who wish to continue to use their substance of choice.     

Long‐term EEG in patients with the ring chromosome 20 epilepsy syndrome

The recognizable electroencephalography (EEG) pattern of ring chromosome 20 epilepsy syndrome can be missing in patients with r(20) chromosomal anomaly, and may be found in patients with frontal lobe epilepsy of other origin. This study aims to search for more specific EEG signs by using long‐term recordings and measuring the duration of paroxysmal anomalies. The series included 12 adult patients with r(20) anomaly, and 12 controls without any chromosomal aberration. We measured the duration of every paroxysmal burst and calculated the sum of their durations for each long‐term EEG recording. We compared patients to controls using the Mann‐Whitney U‐test. Every patient showed long‐lasting paroxysmal EEG bursts, up to 60 min; controls did not show any bursts longer than 60 s (p < 0.0001). The total duration of paroxysmal anomalies was significantly longer in patients (31–692 min) compared to controls (0–48 min) (p < 0.0001). Thus, long‐term recordings enhance the contribution of EEG methods for characterizing the ring 20 chromosome epilepsy syndrome.     

Maturation in auditory event‐related potentials explains variation in language ability in children

Processing of auditory information in the cortex continues to develop into later childhood and adolescence. Recent research has indicated that intraclass correlation (ICC) is the best method for capturing maturation in auditory event‐related potentials (AEPs) of school‐age children. However, the sensitivity of the ICC approach in discerning AEP changes in children has not been consistently demonstrated and positive results have not been replicated. We attempted this replication and further explored whether AEP maturation estimated using the ICC approach predicts cognitive and linguistic abilities in addition to chronological age. We measured AEPs in response to simple tones in groups of 7‐, 8‐, 9‐ and 10‐year olds with typical development (N = 67) and used ICC to estimate the age equivalent of each child's AEP (AEP‐age). Results indicated that ICC differentiated 7‐ to 8‐year‐old children from 9‐ to 10‐year‐old children and that AEP‐age predicted both chronological age and significant, unique variance in language ability, but not in nonverbal IQ. Our findings support the view that auditory organization in children reflects both general developmental maturation and more specific development of language skills, and support the future use of AEP‐age to identify and understand individual differences in brain maturation in typically developing and clinical populations.     

Subclinical temporal EEG seizure pattern in LGI1‐antibody–mediated encephalitis

Leucine‐rich glioma inactived‐1 (LGI1) antibodies are associated with limbic encephalitis and distinctive seizure types, which are typically immunotherapy‐responsive. Although nonspecific electroencephalography (EEG) abnormalities are commonly seen, specific EEG characteristics are not currently understood to be useful for suspecting the clinical diagnosis. Based on initial observations in two patients, we analyzed the clinical features and EEG recordings in a larger series of patients (n = 9) and describe a novel ictal pattern that can suggest the diagnosis of LGI1‐antibody–mediated encephalitis, even in the absence of typical clinical features. As expected, psychiatric and cognitive symptoms were common, as were tonic seizures associated with EEG electrodecremental events (often with the so‐called faciobrachial dystonic semiology). Remarkably, in five patients, a near absence of interictal epileptiform discharges contrasted with frequent subclinical temporal lobe seizures, at times triggered by hyperventilation. This latter EEG pattern may facilitate early diagnosis of this serious but potentially treatable condition.