Inhibition of the LH Surge by Restraint Stress in Cyclic Rats: Studies on the Role of GABAA and GABAB Receptors

There is evidence that stress can alter the activity in the brain of gamma-aminobutyricacid (GABA), a neurotransmitter that has been implicated in the regulation of LH secretion. In the present study the role of GABA in the restraint stress-induced inhibition of the LH surge was investigated in the intact cyclic rat. Intracerebroventricular (icv) administration of the GABAA receptor agonist muscimol (0.1, 0.5 or 1 μg) 5 min before the presumed onset of the pro-oestrous LH surge (at 0900 h) caused a dose dependent suppression of the surge. A single dose of the GABAB receptor agonist baclofen (1 μg; icv) injected at 0855 h postponed the onset of the LH surge, and repeated injections at 0855 and 1130 h suppressed the surge. These data indicate that GABA-ergic activity in the brain can inhibit the LH surge in the cyclic rat via GABAA and GABAB receptors. Pro-oestrous rats were subjected to 5 hrs of restraint starting at 0855 h. Pretreatment with the GABAA receptor antagonist bicuculine (1 μg; icv) at 0840, 0940 and 1040 h or pretreatment with the GABAB receptor antagonist phaclofen (10 μg; icv) at 0840 h were ineffective in preventing the restraint-induced inhibition of the LH surge. The results suggest that GABAA and GABAB receptors are not involved in the inhibitory effect of restraint stress on the LH surge.     

Effects of repetition and configural changes on the development of face recognition processes

We investigated the effect of repetition on recognition of upright, inverted and contrast-reversed target faces in children from 8 to 15 years when engaged in a learning phase/test phase paradigm with target and distractor faces. Early (P1, N170) and late ERP components were analysed Children across age groups performed equally well, and were better at recognizing upright faces. However, teenagers and adults were equally accurate for all three face types. The neurophysiological responses to upright, inverted and negative faces matured until adulthood and showed different effects at different ages. P1 and N170 components were affected by face type at all ages, suggesting early configural disruption on encoding processes regardless of age. Frontal ERPs reflected the difficulty of processing these stimuli. Distinct repetition effects were seen at frontal, temporal frontal and parietal sites, suggesting differential involvement of these brain regions underlying working memory and recognition processes. Thus, a learning phase was sufficient (a) for 8-year-olds to perform as accurately as 15-year-olds and (b) to eliminate face type effects in teenagers and adults, but not in younger children.     

Face inversion and contrast-reversal effects across development: in contrast to the expertise theory

To determine the role of configural changes on the development of face encoding and memory, we investigated face recognition in an n-back repetition task with upright, inverted and contrast-reversed unfamiliar faces in adults and children (8-16 years). Repetitions occurred immediately (0-lag) or after one intervening face (1-lag). Face recognition continued to develop beyond 14-16 years, as shown with hit rates, d' scores and reaction times that all improved with age. Inversion and contrast-reversal effects were found in all subjects but were not more pronounced with increasing age, suggesting no increased reliance on configural processing and thus arguing against the expertise theory of Diamond and Carey (1986). Recognition improved with age in upright but also in inverted and contrast-reversed faces, suggesting a quantitative rather than a qualitative developmental change in face processing. For all age groups, performances decreased and reaction times increased from 0- to 1-lag conditions similarly, suggesting a similar memory component involved in adults' and children's processing. These data suggest gradual quantitative improvements in face processing with age, mainly due to increasing working memory processing capacity.     

Both fearful and happy expressions interact with gaze direction by 200 ms SOA to speed attention orienting

Attention orienting towards a gazed-at location is fundamental to social attention. Whether gaze cues can interact with emotional expressions other than those signalling environmental threat to modulate this gaze cueing, and whether this integration changes over time, remains unclear. With four experiments we demonstrate that, when perceived motion inherent to dynamic displays is controlled for, gaze cueing is enhanced by both fearful and happy faces compared to neutral faces. This enhancement is seen with stimulus-onset asynchronies ranging from 200–700?ms. Thus, gaze cueing can be reliably modulated by positive expressions, albeit to a smaller degree than fearful ones, and this gaze–emotion integration impacts behaviour as early as 200?ms post-cue onset.     

Facial expression discrimination varies with presentation time but not with fixation on features: A backward masking study using eye-tracking

The current study investigated the effects of presentation time and fixation to expression-specific diagnostic features on emotion discrimination performance, in a backward masking task. While no differences were found when stimuli were presented for 16.67 ms, differences between facial emotions emerged beyond the happy-superiority effect at presentation times as early as 50 ms. Happy expressions were best discriminated, followed by neutral and disgusted, then surprised, and finally fearful expressions presented for 50 and 100 ms. While performance was not improved by the use of expression-specific diagnostic facial features, performance increased with presentation time for all emotions. Results support the idea of an integration of facial features (holistic processing) varying as a function of emotion and presentation time.     

Effects of peripheral eccentricity and head orientation on gaze discrimination

Visual search tasks support a special role for direct gaze in human cognition, while classic gaze judgement tasks suggest the congruency between head orientation and gaze direction plays a central role in gaze perception. Moreover, whether gaze direction can be accurately discriminated in the periphery using covert attention is unknown. In the present study, individual faces in frontal and in deviated head orientations with a direct or an averted gaze were flashed for 150 ms across the visual field; participants focused on a centred fixation while judging the gaze direction. Gaze discrimination speed and accuracy varied with head orientation and eccentricity. The limit of accurate gaze discrimination was less than ±6° eccentricity. Response times suggested a processing facilitation for direct gaze in fovea, irrespective of head orientation, however, by ±3° eccentricity, head orientation started biasing gaze judgements, and this bias increased with eccentricity. Results also suggested a special processing of frontal heads with direct gaze in central vision, rather than a general congruency effect between eye and head cues. Thus, while both head and eye cues contribute to gaze discrimination, their role differs with eccentricity.     

Combined effects of inversion and feature removal on N170 responses elicited by faces and car fronts

The face-sensitive N170 is typically enhanced for inverted compared to upright faces. Itier, Alain, Sedore, and McIntosh (2007) recently suggested that this N170 inversion effect is mainly driven by the eye region which becomes salient when the face configuration is disrupted. Here we tested whether similar effects could be observed with non-face objects that are structurally similar to faces in terms of possessing a homogeneous within-class first-order feature configuration. We presented upright and inverted pictures of intact car fronts, car fronts without lights, and isolated lights, in addition to analogous face conditions. Upright cars elicited substantial N170 responses of similar amplitude to those evoked by upright faces. In strong contrast to face conditions however, the car-elicited N170 was mainly driven by the global shape rather than the presence or absence of lights, and was dramatically reduced for isolated lights. Overall, our data confirm a differential influence of the eye region in upright and inverted faces. Results for car fronts do not suggest similar interactive encoding of eye-like features and configuration for non-face objects, even when these objects possess a similar feature configuration as faces.     

The role of eyes in early face processing: a rapid adaptation study of the inversion effect

The current study employed a rapid adaptation procedure to test the neuronal mechanisms of the face inversion effect (FIE) on the early face-sensitive event-related potential (ERP) component N170. Five categories of face-related stimuli (isolated eyes, isolated mouths, eyeless faces, mouthless faces, and full faces) and houses were presented in upright and inverted orientations as adaptors for inverted full face test stimuli. Strong adaptation was found for all face-related stimuli except mouths. The adaptation effect was larger for inverted than upright stimuli, but only when eyes were present. These results underline an important role of eyes in early face processing. A mechanism of eye-dependent orientation sensitivity during the structural encoding stage of faces is proposed.     

Individual differences in the emotional modulation of gaze-cuing

Gaze-cuing refers to the spontaneous orienting of attention towards a gazed-at location, characterised by shorter response times to gazed-at than non-gazed at targets. Previous research suggests that processing of these gaze cues interacts with the processing of facial expression cues to enhance gaze-cuing. However, whether only negative emotions (which signal potential threat or uncertainty) can enhance gaze-cuing is still debated, and whether this emotional modulation varies as a function of individual differences still remains largely unclear. Combining data from seven experiments, we investigated the emotional modulation of gaze-cuing in the general population as a function of participant sex, and self-reported subclinical trait anxiety, depression, and autistic traits. We found that (i) emotional enhancement of gaze-cuing can occur for both positive and negative expressions, (ii) the higher the score on the Attention to Detail subscale of the Autism Spectrum Quotient, the smaller the emotional enhancement of gaze-cuing, especially for happy expressions, and (iii) emotional modulation of gaze-cuing does not vary as a function of participant anxiety, depression or sex, although women display an overall larger gaze-cuing effect than men.