Hypothyroidism and major depression: a common executive dysfunction?

Little is known about the possible link between the cognitive disorders associated with hypothyroidism and those encountered in depression. This study examines attentional and executive functions as well as the intensity of anxiety and depressive symptoms in hypothyroidism and major depression and the possible link between these symptoms and cognitive disturbances. This study confirms the existence of psychomotor slowing associated with attentional and executive disturbance in major depression as well as in hypothyroidism. However, while depressed subjects manifested a conscious bias with material of negative emotional valence, no such bias was found in the hypothyroid subjects. While the hypothyroid state is accompanied by anxiety/depressive symptoms, it seems that the latter are too discrete for an attentional bias to be observed with material with a negative emotional valence.

Anxiety and depression, attention, and executive functions in hypothyroidism.

BACKGROUND: Divergences in cognitive disturbances in hypothyroidism reported in the literature are a result of a methodological bias. METHODS: By using a precise methodology, we examined attention and executive functions in hypothyroidism, verified the presence of anxiety and depressive symptoms in hypothyroidism, and examined the possible link between these symptoms and the cognitive disturbances (searching for attentional bias for words with a negative emotional valence). We administered a battery of cognitive tests to 23 participants who had undergone thyroidectomy for thyroid carcinoma: for the first time in an euthyroid state, then 3 weeks later (still in the euthyroid state) to assess the test/retest effect, and finally 4 weeks later in an hypothyroid state. We compared their performance with that of a group of 26 control participants who were also administered the same cognitive tests, also 3 times. RESULTS: In hypothyroidism, the thyroid participants were more anxious and depressed than the controls and presented attentional and executive disturbances that reflected general slowing and difficulties in using their capacities of inhibition. However, they did not exhibit an attentional bias for words with a negative emotional valence. CONCLUSIONS: Contrary to what was expected, symptoms of anxiety and not symptoms of depression interfered with the cognitive performance of participants in hypothyroidism.

The Ponzo illusion with auditory substitution of vision in sighted and early-blind subjects.

We tested the effects of using a prosthesis for substitution of vision with audition (PSVA) on sensitivity to the Ponzo illusion. The effects of visual experience on the susceptibility to this illusion were also assessed. In one experiment, both early-blind and blindfolded sighted volunteers used the PSVA to explore several variants of the Ponzo illusion as well as control stimuli. No effects of the illusion were observed. The results indicate that subjects focused their attention on the two central horizontal bars of the stimuli, without processing the contextual cues that convey perspective in the Ponzo figure. In a second experiment, we required subjects to use the PSVA to consider the two converging oblique lines of the stimuli before comparing the length of the two horizontal bars. Here we were able to observe susceptibility to the Ponzo illusion in the sighted group, but to a lesser extent than in a sighted non-PSVA control group. No clear effect of the ilusion was obtained in early-blind subjects. These results suggest that, at least in sighted subjects, perception obtained with the PSVA shares perceptual processes with vision. Visual experience appears mandatory for a Ponzo illusion to occur with the PSVA.

When audition alters vision: an event-related potential study of the cross-modal interactions between faces and voices.

Ten healthy volunteers took part in this event-related potential (ERP) study aimed at examining the electrophysiological correlates of the cross-modal audio-visual interactions in an identification task. Participants were confronted either to the simultaneous presentation of previously learned faces and voices (audio-visual condition; AV), either to the separate presentation of faces (visual, V) or voices (auditive, A). As expected, an interference effect of audition on vision was observed at a behavioral level, as the bimodal condition was performed more slowly than the visual condition. At the electrophysiological level, the subtraction (AV - (A + V)) gave prominence to three distinct cerebral activities: (1) a central positive/posterior negative wave around 110 ms, (2) a central negative/posterior positive wave around 170 ms, AND (3) a central positive wave around 270 ms. These data suggest that cross-modal cerebral interactions could be independent of behavioral facilitation or interference effects. Moreover, the implication of unimodal and multisensory convergence regions in these results, as suggested by a source localization analysis, is discussed.

Human gender differences in an emotional visual oddball task: an event-related potentials study.

Pictures from the Ekman and Friesen series were used in an event-related potentials study to define the timing of occurrence of gender differences in the processing of positive (happy) and negative (fear) facial expressions. Ten male and 10 female volunteers were confronted with a visual oddball design, in which they had to detect, as quickly as possible, deviant happy or fearful faces amongst a train of standard stimuli (neutral faces). Behavioral results suggest that men and women detected fearful faces more quickly than happy ones. The main result is that the N2b component, functionally considered as an attentional orienting mechanism, was delayed in men for happy stimuli as compared with fearful ones. Gender differences observed in the processing of emotional stimuli could then originate at the attentional level of the information processing system.

The electrophysiological correlates sustaining the retrieval of face-name associations: an ERP study.

An ERP study on 9 healthy participants was carried out to temporally constrain the neural network proposed by Campanella et al. (2001) in a PET study investigating the cerebral areas involved in the retrieval of face-name associations. Three learning sessions served to familiarize the participants with 24 face-name associations grouped in 12 male/female couples. During EEG recording, participants were confronted with four experimental conditions, requiring the retrieval of previously learned couples on the basis of the presentation of name-name (NN), face-face (FF), name-face (NF), or face-name (FN) pairs of stimuli. The main analysis of this experiment consisted in the subtraction of the nonmixed conditions (NN and FF) from the mixed conditions (NF and FN). It revealed two main ERP components: a negative wave peaking at left parieto-occipital sites around 285 ms and its positive counterpart recorded at left centro-frontal electrodes around 300 ms. Moreover, a dipole modeling using three dipoles whose localization corresponded to the three cerebral areas observed in the PET study (left inferior frontal gyrus, left medial frontal gyrus, left inferior parietal lobe) explained more than 90% of the variance of the results. The complementarity between anatomical and neurophysiological techniques allowed us to discuss the temporal course of these cerebral activities and to propose an interactive and original anatomo-temporal model of the retrieval of face-name associations.

Discrimination of emotional facial expressions in a visual oddball task: an ERP study.

Several ERP studies have shown an orienting complex, the N2/P3a, associated to the detection of stimulus novelty. Its role consists in preparing the organism to process and react to biologically prepotent stimuli. Whether this N2/P3a: (1) could be obtained with complex visual stimuli, such as with emotional facial expressions; and (2) could take part in a complex discrimination process has yet to be determined. To investigate this issue, event-related potentials were recorded in response to repetitions of a particular facial expression (e.g. sadness) and in response to two different deviant (rare) stimuli, one depicting the same emotion as the frequent stimulus, while the other depicted a different facial expression (e.g. fear). As expected, deviant stimuli evoked an N2/P3a complex of larger amplitude than frequent stimuli. But more interestingly, when the deviant stimulus depicted the same emotion as the frequent stimulus the N2/P3a was delayed compared to the response elicited by the different-emotion deviant. The N2/P3a was thus implicated in the detection of physical facial changes, with a higher sensitivity to changes related to a new different emotional content, perhaps leading to faster adaptive reactions.

Categorical perception of happiness and fear facial expressions: an ERP study.

Behavioral studies have shown that two different morphed faces perceived as reflecting the same emotional expression are harder to discriminate than two faces considered as two different ones. This advantage of between-categorical differences compared with within-categorical ones is classically referred as the categorical perception effect. The temporal course of this effect on fear and happiness facial expressions has been explored through event-related potentials (ERPs). Three kinds of pairs were presented in a delayed same-different matching task: (1) two different morphed faces perceived as the same emotional expression (within-categorical differences), (2) two other ones reflecting two different emotions (between-categorical differences), and (3) two identical morphed faces (same faces for methodological purpose). Following the second face onset in the pair, the amplitude of the bilateral occipito-temporal negativities (N170) and of the vertex positive potential (P150 or VPP) was reduced for within and same pairs relative to between pairs. This suggests a repetition priming effect. We also observed a modulation of the P3b wave, as the amplitude of the responses for the between pairs was higher than for the within and same pairs. These results indicate that the categorical perception of human facial emotional expressions has a perceptual origin in the bilateral occipito-temporal regions, while typical prior studies found emotion-modulated ERP components considerably later.

Association of the distinct visual representations of faces and names: a PET activation study.

A PET study of seven normal individuals was carried out to investigate the neural populations involved in the retrieval of the visual representation of a face when presented with an associated name, and conversely. Face-name associations were studied by means of four experimental matching conditions, including the retrieval of previously learned (1) name-name (NN), (2) face-face (FF), (3) name-face (NF), and (4) face-name (FN) associations, as well as a resting scan with eyes closed. Before PET images acquisition, subjects were presented with 24 unknown face-name associations to encode in 12 male/female couples. During PET scanning, their task was to decide whether the presented pair was a previously learned association. The right fusiform gyrus was strongly activated in FF condition as compared to NN and Rest conditions. However, no specific activations were found for NN condition relative to FF condition. A network of three areas distributed in the left hemisphere, both active in (NF-FF) and (FN-NN) comparisons, was interpreted as the locus of the integration of visual faces and names representations. These three regions were localized in the inferior frontal gyrus (BA 45), the medial frontal gyrus (BA 6) and the supramarginal gyrus of the inferior parietal lobe (BA 40). An interactive model accounting for these results, with BA 40 seen as an amodal binding region, is proposed.

Right N170 modulation in a face discrimination task: an account for categorical perception of familiar faces.

Behavioral studies have shown that two different morphed faces belonging to the same identity are harder to discriminate than two faces stemming from two different identities. The temporal course of this categorical perception effect has been explored through event-related potentials. Three kinds of pairs were presented in a matching task: (1) two different morphed faces representing the same identity (within), (2) two other faces representing two different identities (between), and (3) two identical morphed faces (same). Following the second face onset in the pair, the amplitude of the right occipitotemporal negativity (N170) was reduced for within and same pairs as compared with between pairs, suggesting an identity priming effect. We also observed a modulation of the P3b wave, as the amplitude of the responses for within pairs was higher than for between and same pairs, suggesting a higher complexity of the task for within pairs. These results indicate that categorical perception of human faces has a perceptual origin in the right occipitotemporal hemisphere.

The fate of global precedence with age.

The literature is virtually devoid of studies examining the effect of aging on the "global precedence" effect (Navon, D. [1977]. Cognitive Psychology, 9, 353-383). In this paradigm, global letters formed with local letters are shown, and the subject has to recognize either the local or the global letters. The relation between the global and the local letters is either congruent, neutral, or conflicting. Five experiments are reported, with five sets of 16 young and five sets of 16 elderly, healthy, adult subjects. The global precedence effect was observed in both age groups in the basic perceptual experiment as designed by Navon (Experiment 1). In addition, young and elderly subjects were able to process separately the global and the local shapes when attention was not directed towards a specific level (Experiment 1a). However, subpopulations emerged, especially in the elderly, depending on their ability to "resist" to the interference of the global shape upon the processing of the local form. This could support the few indirect published data suggesting that global precedence tends to diminish or to disappear with age. In experiments 2 and 2a, subjects were retained only if they did process the local level better than at random. Global precedence was confirmed in both young and elderly subjects. Again, elderly subjects manifested an increased sensitivity to interference. Moreover, a general effect of age remained, even in the control (neutral) conditions, suggesting difficulties of encoding in elderly. Therefore, in Experiment 3, encoding conditions of both age groups were equated by increasing exposure duration of the material for elderly. Subjects of Experiment 3 were also submitted to a Stroop test, to verify whether the increased sensitivity to interference in the elderly was specific to the "Navon task" or the expression of a general effect of aging on inhibition mechanisms. The global precedence phenomenon was observed in young and elderly subjects, with no sign of an effect of age under these conditions; in elderly, furthermore, the interference effect did not appear to result from a general aspecific deficit of inhibition mechanisms. It thus appears that the global precedence phenomenon resists well the effects of aging, but that subpopulations of elderly subjects should be considered in future studies.

Effects of aging on the generation of mental images.

Image generation is one component of mental imagery, and consists in the activation of stored visual information in long-term memory to sequentially create a temporary pattern on a visuospatial short-term memory display. Little is known about the fate of image generation over the human life span. In the present study, 165 healthy participants aged 18 to 80 years were enrolled for an image generation task to image an uppercase letter in response to its lowercase version displayed as the cue, and to decide if a displayed probe would be near to or on the image. Uppercase letters were simple versus complex, and the probe appeared in a region of the uppercase letter that is generated early versus late. Comparative analyses (ANOVAs) on accuracy and correct latency confirmed the sequential nature of image generation, and showed a detrimental and linear effect of aging only on the activation subprocess. Structural analyses (LISREL) revealed, however, that these effects of age were entirely mediated by inhibition mechanisms, speed of processing, and working memory.

Number processing and calculation in a case of visual agnosia.

We describe the performance of a brain-damaged subject who suffered from visual agnosia leading to major difficulties in generating and exploiting visual representations from long-term memory. His performance in a physical judgement task in which he was required to answer questions about the visual shapes of Arabic numerals reflected his agnosic problems. However, he showed no impairment in usual number processing and calculation tasks. This case shows that, despite some commonalities in number and object processing, actual numerical processes are not affected by visual agnosia and can be preserved even when fine visual processes are impaired.

The N170 occipito-temporal component is delayed and enhanced to inverted faces but not to inverted objects: an electrophysiological account of face-specific processes in the human brain.

Behavioral studies have shown that picture-plane inversion impacts face and object recognition differently, thereby suggesting face-specific processing mechanisms in the human brain. Here we used event-related potentials to investigate the time course of this behavioral inversion effect in both faces and novel objects. ERPs were recorded for 14 subjects presented with upright and inverted visual categories, including human faces and novel objects (Greebles). A N170 was obtained for all categories of stimuli, including Greebles. However, only inverted faces delayed and enhanced N170 (bilaterally). These observations indicate that the N170 is not specific to faces, as has been previously claimed. In addition, the amplitude difference between faces and objects does not reflect face-specific mechanisms since it can be smaller than between non-face object categories. There do exist some early differences in the time-course of categorization for faces and non-faces across inversion. This may be attributed either to stimulus category per se (e.g. face-specific mechanisms) or to differences in the level of expertise between these categories.

[A comparison between group-average and individual evoked potential analysis]. / Etude comparative en potentiels évoqués des données fournies par le biais d'analyses de groupes et individuelles.

PURPOSE: Event-related potentials (ERPs) studies in human subjects have shown inter-individual response variations, probably linked to anatomical and functional brain disparities. The present study was conducted to compare the results obtained by a standard grand-average method and a single subject analysis of VEPs to faces. MATERIAL AND METHOD: Fifty-eight channel ERPs (analysis time: 1,024 ms) were recorded in 13 normal volunteers during gender or familiarity judgements on unknown and known faces, as well as on a control task using meaningless patterns. Data were then submitted to individual and group averages. RESULTS AND CONCLUSION: Three activities were identified by both procedures: a P1/N1 complex, a vertex positive potential (P2 or VPP) associated with a temporal negativity, and a N2 negativity. These peaks displayed a marked inter-individual topographical variability. Regarding the outcome of statistical analyses, a certain number of differences were found: on P1, in which individual analyses revealed a strong effect of experimental conditions, while the grand-average method did not; on VPP, in which grand-average analyses suggested an interaction between experimental conditions, face familiarity and cerebral lateralization, while individual analyses did not; and on N2, in which grand-average data showed a clear lateralization effect, while individual analyses did not. A P3 component (Pz, 250 ms) was also defined in grand-average data, but could not be clearly described in individual data. Statistical analyses on this P3 component were thus only performed on group data and revealed a right lateralization and an interaction between face familiarity and experimental conditions. These findings confirmed the existence of a marked topographical variability of ERPs to face and, therefore, question the validity of grand-average studies. Moreover, these results suggest a better efficiency of individual analyses for studying short and middle-latency peaks, while grand-averages appear to be better suited for studying late components.

Spatio-temporal localization of the face inversion effect: an event-related potentials study.

Event-related potentials (ERPs) from 58 electrodes at standard EEG sites were recorded while 14 subjects performed a delayed-matching task on normal and inverted faces. A large and single difference between normal and inverted face processing was observed at occipito-temporal sites about 160 ms following stimulus onset, mainly in the right hemisphere (RH). Although the topographies indicate that similar areas are involved at this latency in processing the two types of stimuli, the electrophysiological activity, which corresponds to the previously described N170, was larger and delayed for inverted as compared to normal face processing. These results complement and specify, at a neural level, previous behavioral and divided visual field studies which have suggested that the loss of configural face information by inversion may slow down and increase the difficulty of face processing, particularly in the RH.

Task modulation of brain activity related to familiar and unfamiliar face processing: an ERP study.

In order to investigate stimulus-related and task-related electrophysiological activity relevant for face processing, event-related potentials (ERPs) from 58 electrodes at standard EEG sites were recorded while subjects performed a simple visual discrimination (control) task, in addition to various face processing tasks: recognition of previously learned faces and gender decision on familiar and unfamiliar faces. Three electrophysiological components or dipolar complex were recorded in all subjects: an occipital early component (P1, around 110 ms); a vertex positive potential (VPP; around 158 ms) which appeared to be specific to faces; and a negative central component, N2 (around 230 ms). Parametric analysis and source localization were applied to these components by means of a single-subject analysis methodology. No effect of familiarity was observed on any of these early component. While the VPP appears to be independent of the kind of processing performed, face task modulations of the early P1 and the N2 were observed, with a higher amplitude for the recognition than for the gender discrimination task. An attentional modulation of early visual areas is proposed for the first effect (P1 modulation), while the N2 seems to be related to general visual memory processing. This study strongly suggests that the VPP reflects an early visual stage of face processing in the fusiform gyrus that is strictly stimulus-related and independent of familiarity. It also shows that source localization algorithms may give reliable solutions on single subject averages for early visual components despite high inter-subject variability of the surface characteristics of ERPs.

Effect of familiarity on the processing of human faces.

Most brain imaging studies on face perception have investigated the processing of unknown faces and addressed mainly the question of specific face processing in the human brain. The goal of this study was to highlight the effects of familiarity on the visual processing of faces. Using [15O]water 3D Positron Emission Tomography, regional cerebral blood flow distribution was measured in 11 human subjects performing an identical task (gender categorization) on both unknown and known faces. Subjects also performed two control tasks (a face recognition task and a visual pattern discrimination task). They were scanned after a training phase using videotapes during which they had been familiarized with and learned to recognize a set of faces. Two major results were obtained. On the one hand, we found bilateral activations of the fusiform gyri in the three face conditions, including the so-called fusiform-face area, a region in the right fusiform gyrus specifically devoted to face processing. This common activation suggests that different cognitive tasks performed on known and unknown faces require the involvement of this fusiform region. On the other hand, specific regional cerebral blood flow changes were related to the processing of known and unknown faces. The left amygdala, a structure involved in implicit learning of visual representations, was activated by the categorization task on unknown faces. The same task on known faces induced a relative decrease of activity in early visual areas. These differences between the two categorization tasks reveal that the human brain processes known and unknown faces differently.

Short-term memory for faces: ageing and the serial position effect.

Properties of short-term memory for faces (Exp. 1) were investigated in 40 young and 30 elderly persons and compared with short-term memory for non-verbal shapes (Exp. 2) with 30 new persons in a young group and an elderly one. Young subjects displayed a U-shaped curve for both kinds of stimuli, and elderly subjects displayed a U-shaped curve, but the recency effect was abolished for faces (in one condition). This suggests a possible specific short-term store for faces.

The visuospatial sketchpad for mental images: testing the multicomponent model of working memory.

In the model of Baddeley (Working Memory, Oxford University Press, Oxford, 1986), one function of the visuospatial sketchpad (VSSP) component of working memory is to allow the processing of mental images. Properties of the VSSP were investigated by means of the usual dual-task paradigm (to search for interference from the other components of working memory, i.e., the articulatory loop and the central executive), applied to three distinct subprocesses of mental imagery (Kosslyn, 1994 Image and Brain. MIT Press, Cambridge, MA): image generation (Experiment 1), image maintenance (Experiment 2), and image rotation (Experiment 3). First, in the control condition (no interference task) of each experiment, we replicated the effects of stimulus or task complexity already reported. Second, no interference from the articulatory loop was observed. Third, maintenance of images appeared free from any interference. And fourth, generation and rotation tasks were interfered to a greater extent by the central executive than by the involvement of the VSSP in a secondary task. These observations (a) support the dissociation between the articulatory loop and the VSSP, (b) suggest an important use of central attentional resources in the generation and rotation of mental images, (c) would support the distinction between visual and spatial components in the structure of working memory, and (d) suggest the dissociation of the VSSP into two subcomponents: a passive visuospatial store and an active device for recapitulating visuospatial information.