Early glycinergic axon contact with the Mauthner neuron during zebrafish development

One important aspect of empathy is a “resonance mechanism”, which includes emotional cue detection, facial mimicry (measured by electromyography, EMG) and a specific cortical response. This study explored the convergence of these three measures of affective empathy. The twenty students who took part in the study were required to empathise with the situation by entering into the other person's situation. The four emotions portrayed were anger, fear, happiness, and neutral, and the subjects were instructed to make a two-alternative response (emotion or no emotion) to each emotion. A repeated transcranial magnetic stimulation was used to produce a temporary inhibition of the medial prefrontal cortex (MPFC). The results support the hypothesis that there is a direct relationship between emotional cue recognition, EMG-measured facial response and prefrontal activity. First, both facial expression detection and autonomic mimicry in reaction to emotional faces were systematically modulated in response to inhibition of the MPFC. Second, the MPFC was implicated in facial cue detection and the subsequent autonomic response because an impaired performance on both measures was observed when this brain area was inhibited. Third, this effect increased when negative-valenced stimuli (angry and fearful faces) were presented to the subjects. These results revealed a significant effect of the MPFC on both cue detection and facial mimicry that was distinctly related to different types of emotions.     

Subnormal short-latency facial mimicry responses to dynamic emotional facial expressions in male adolescents with disruptive behavior disorders and callous-unemotional traits

Using still pictures of emotional facial expressions as experimental stimuli, reduced amygdala responses or impaired recognition of basic emotions were repeatedly found in people with psychopathic traits. The amygdala also plays an important role in short-latency facial mimicry responses. Since dynamic emotional facial expressions may have higher ecological validity than still pictures, we compared short-latency facial mimicry responses to dynamic and static emotional expressions between adolescents with psychopathic traits and normal controls. Facial EMG responses to videos or still pictures of emotional expressions (happiness, anger, sadness, fear) were measured. Responses to 500-ms dynamic expressions in videos, as well as the subsequent 1500-ms phase of maximal (i.e., static) expression, were compared between male adolescents with disruptive behavior disorders and high (n = 14) or low (n = 17) callous-unemotional (CU) traits, and normal control subjects (n = 32). Responses to still pictures were also compared between groups. EMG responses to dynamic expressions were generally significantly smaller in the high-CU group than in the other two groups, which generally did not differ. These group differences gradually emerged during the 500-ms stimulus presentation period but in general they were already seen a few hundred milliseconds after stimulus onset. Group differences were absent during the 1500-ms phase of maximal expression and during exposure to still pictures. Subnormal short-latency mimicry responses to dynamic emotional facial expressions in the high-CU group might have negative consequences for understanding emotional facial expressions of others during daily life when human facial interactions are primarily dynamic.     

Face emotion labeling deficits in children with bipolar disorder and severe mood dysregulation

Children with narrow phenotype bipolar disorder (NP-BD; i.e., history of at least one hypomanic or manic episode with euphoric mood) are deficient when labeling face emotions. It is unknown if this deficit is specific to particular emotions, or if it extends to children with severe mood dysregulation (SMD; i.e., chronic irritability and hyperarousal without episodes of mania). Thirty-nine NP-BD, 31 SMD, and 36 control subjects completed the emotional expression multimorph task, which presents gradations of facial emotions from 100% neutrality to 100% emotional expression (happiness, surprise, fear, sadness, anger, and disgust). Groups were compared in terms of intensity of emotion required before identification occurred and accuracy. Both NP-BD and SMD youth required significantly more morphs than controls to label correctly disgusted, surprised, fearful, and happy faces. Impaired face labeling correlated with deficient social reciprocity skills in NP-BD youth and dysfunctional family relationships in SMD youth. Compared to controls, patients with NP-BD or SMD require significantly more intense facial emotion before they are able to label the emotion correctly. These deficits are associated with psychosocial impairments. Understanding the neural circuitry associated with face-labeling deficits has the potential to clarify the pathophysiology of these disorders.     

Autonomic arousal explains social cognitive abilities in high-functioning adults with autism spectrum disorder

Empirical research into behavioural profiles and autonomic responsivity in individuals with autism spectrum disorders (ASDs) is highly variable and inconsistent. Two preliminary studies of children with ASDs suggest that there may be subgroups of ASDs depending on their resting arousal levels, and that these subgroups show different profiles of autonomic responsivity. The aim of the present study was to determine whether (i) adults with high-functioning ASDs may be separated into subgroups according to variation in resting arousal; and (ii) these ASD arousal subgroups differ in their behavioural profiles for basic emotion recognition, judgements of trustworthiness, and cognitive and affective empathy. Thirty high-functioning adults with ASDs and 34 non-clinical controls participated. Resting arousal was determined as the average skin conductance (SCL) across a 2 min resting period. There was a subgroup of ASD adults with significantly lower resting SCL. These individuals demonstrated poorer emotion recognition, tended to judge faces more negatively, and had atypical relationships between SCL and affective empathy. In contrast, low cognitive empathy was a feature of all ASD adults. These findings have important implications for clinical interventions and future studies investigating autonomic functioning in ASDs.     

Effects of reversible inactivation by cooling of the primate face motor cortex on the performance of a trained tongue-protrusion task and a trained biting task

1. Intracortical microstimulation (ICMS) and surface stimulation studies of primate face motor cortex have shown an extensive representation within face motor cortex devoted to movements of the tongue and face; only a very small representation for jaw-closing movements has ever been demonstrated. These data suggest that face motor cortex plays a critical role in the generation of tongue and facial movements but is less important in the generation of jaw-closing movements. Our aim was to determine whether disruption of primate face motor cortical function would indeed interfere with the generation of tongue movements but would not interfere with the generation of jaw-closing movements. 2. The face motor cortex was reversibly inactivated with the use of cooling in two monkeys that were trained to perform both a tongue-protrusion task and a biting task. Recording of single neuronal activity in the cortex beneath the thermode confirmed the reversible inactivation of the cortex. Each task involved a series of trials in which the monkey was required to produce a preset force level for a 0.5-s force holding period; the monkey received a fruit-juice reward if it successfully completed a task trial. Cooling of the ICMS-defined face motor cortex was achieved bilaterally or, in one experiment, unilaterally by circulating coolant through thermodes placed either on intact dura overlying face motor cortex in both monkeys or directly on the exposed pia in one of the monkeys;thermode temperature was lowered to 3-5 degrees C during cooling. Electromyographic (EMG) recordings were also made from masseter, genioglossus, and digastric muscles. 3. During bilateral cooling of the thermodes on the dura overlying the face motor cortex, there was a significant reduction in the success rates for the performance of the tongue-protrusion task in comparison with control series of trials (i.e., precool and postcool) in which the thermodes were kept at 37 degrees C. Quantitative analyses of force and EMG activity showed that the principal deficit was an inability of each monkey to exert sufficient force with its tongue for a sufficient length of time onto the tongue-protrusion task transducer; this deficit was paralleled by a reduction in the level of genioglossus and digastric EMG activity. At 4 min after commencement of rewarming, task performance had returned to control, precool levels.(ABSTRACT TRUNCATED AT 400 WORDS)     

Hemispheric asymmetry and theory of mind: Is there an association?

Introduction. In autism and schizophrenia attenuated/atypical functional hemispheric asymmetry and theory of mind impairments have been reported, suggesting common underlying neuroscientific correlates. We here investigated whether impaired theory of mind performance is associated with attenuated/atypical hemispheric asymmetry. An association may explain the co-occurrence of both dysfunctions in psychiatric populations.

Methods. Healthy participants (n=129) performed a left hemisphere (lateralised lexical decision task) and right hemisphere (lateralised face decision task) dominant task as well as a visual cartoon task to assess theory of mind performance.

Results. Linear regression analyses revealed inconsistent associations between theory of mind performance and functional hemisphere asymmetry: enhanced theory of mind performance was only associated with (1) faster right hemisphere language processing, and (2) reduced right hemisphere dominance for face processing (men only).

Conclusions The majority of non-significant findings suggest that theory of mind and functional hemispheric asymmetry are unrelated. Instead of “overinterpreting” the two significant results, discrepancies in the previous literature relating to the problem of the theory of mind concept, the variety of tasks, and the lack of normative data are discussed. We also suggest how future studies could explore a possible link between hemispheric asymmetry and theory of mind.     

Synergists activation pattern of the quadriceps muscle differs when performing sustained isometric contractions with different EMG biofeedback

The aims of the present study were to examine (1) endurance time and (2) activation pattern of vastus lateralis (VL), vastus medialis (VM) and rectus femoris (RF) muscles during fatiguing isometric knee extensions performed with different EMG biofeedbacks. Thirteen men (27 ± 5 year) volunteered to participate in three experimental sessions. Each session involved a submaximal isometric contraction held until failure at an EMG level corresponding to 40% maximal voluntary contraction torque (MVC), with visual EMG biofeedback provided for either (1) RF muscle (RF task), (2) VL and VM muscles (Vasti task) or (3) the sum of the VL, VM and RF muscles (Quadriceps task). EMG activity of VL, VM and RF muscles was recorded during each of the three tasks and further analyzed. Time to task failures and MVC loss (P < 0.001) after exercises were similar (P > 0.05) between the three sessions (182 s and ∼28%, respectively) (P > 0.05). Moreover, the magnitude of central and peripheral fatigue was not different at failure of the three tasks. Activation pattern was similar for knee extensors at the beginning of each task (P > 0.05). However, RF EMG activity decreased (P < 0.05) during the Vasti and the Quadriceps tasks (from ∼33 to ∼25% maximal EMG), whereas vasti EMG activity remained constant during the RF task (∼41% maximal EMG). These findings suggest that (1) task failure occurs when sustaining a submaximal level of EMG activity for as long as possible and (2) CNS is not able to differentiate descending drive to the different heads of the quadriceps at the beginning of a sustained contraction, despite a different activation pattern for the bi-articular RF muscle compared to the mono-articular vasti muscles during fatigue.     

Recognition of Facially Expressed Emotions in Patients with Fibromyalgia Syndrome

The study investigated the ability to identify facially expressed emotions in fibromyalgia syndrome (FMS) and its association with clinical parameters. Thirty-five FMS patients and 35 healthy controls accomplished a face recognition task. Additionally, pain severity, alexithymia, depression, anxiety, psychiatric co-morbidity and medication use were assessed. The patients displayed reduced task performance in terms of more misclassifications of emotional expressions than controls. Pain severity, alexithymia, depression and anxiety were inversely related to recognition performance, with pain severity accounting for the largest portion of test score variance. Psychiatric co-morbidity and medication had no impact on performance. The study documented impaired emotion recognition in FMS, which may contribute to the interpersonal difficulties and reduced social functioning related to this condition. As potential mechanisms mediating the occurrence of the deficits, altered affective processing due to interoceptive impairment as well as interference of central nervous nociceptive activity with cognitive and emotional processing are discussed.     

Electromyographic responses to emotional facial expressions in 6-7year olds: A feasibility study

Preliminary studies have demonstrated that school-aged children (average age 9-10years) show mimicry responses to happy and angry facial expressions. The aim of the present study was to assess the feasibility of using facial electromyography (EMG) as a method to study facial mimicry responses in younger children aged 6-7years to emotional facial expressions of other children. Facial EMG activity to the presentation of dynamic emotional faces was recorded from the corrugator, zygomaticus, frontalis and depressor muscle in sixty-one healthy participants aged 6-7years. Results showed that the presentation of angry faces was associated with corrugator activation and zygomaticus relaxation, happy faces with an increase in zygomaticus and a decrease in corrugator activation, fearful faces with frontalis activation, and sad faces with a combination of corrugator and frontalis activation. This study demonstrates the feasibility of measuring facial EMG response to emotional facial expressions in 6-7year old children.     

Hemispheric asymmetry and theory of mind: Is there an association?

Introduction. In autism and schizophrenia attenuated/atypical functional hemispheric asymmetry and theory of mind impairments have been reported, suggesting common underlying neuroscientific correlates. We here investigated whether impaired theory of mind performance is associated with attenuated/atypical hemispheric asymmetry. An association may explain the co-occurrence of both dysfunctions in psychiatric populations. Methods. Healthy participants (n=129) performed a left hemisphere (lateralised lexical decision task) and right hemisphere (lateralised face decision task) dominant task as well as a visual cartoon task to assess theory of mind performance. Results. Linear regression analyses revealed inconsistent associations between theory of mind performance and functional hemisphere asymmetry: enhanced theory of mind performance was only associated with (1) faster right hemisphere language processing, and (2) reduced right hemisphere dominance for face processing (men only). Conclusions The majority of non-significant findings suggest that theory of mind and functional hemispheric asymmetry are unrelated. Instead of "overinterpreting" the two significant results, discrepancies in the previous literature relating to the problem of the theory of mind concept, the variety of tasks, and the lack of normative data are discussed. We also suggest how future studies could explore a possible link between hemispheric asymmetry and theory of mind.     

The facilitative effect of facial expression on the self-generation of emotion.

Twenty-seven female undergraduates completed three tasks: (1) feel four emotions (happiness, sadness, anger, peacefulness); (2) express these emotions, without trying to feel them; and (3) feel and express clearly these four emotions. During each trial subjects pressed a button to indicate when they had reached the required state, and the latency from emotion cue to button press was measured. Heart rate, skin conductance and EMG from four facial sites (brow, cheek, jaw and mouth) were recorded for 15 s before and after the button press and during a baseline period prior to each trial. Self-reports were obtained after each trial. Facial EMG and patterns of autonomic arousal differentiated among the four emotions within each task. Shorter self-generation latency in the Feel-and-Show versus the Feel condition indicated the facilitative effect of facial expression on the self-generation of emotion. Furthermore, the presence of autonomic changes and self-reported affect in the Show condition supports the sufficiency version of the facial feedback hypothesis. The self-generation method employed as an emotion elicitor was shown to reliably induce emotional reactions and is proposed as a useful technique for the elicitation of various emotional states in the laboratory.     

The impact of social context on mimicry

Facial mimicry, the tendency to imitate other's facial expressions, has frequently been described as a reflex-like mechanism that function independent of the relationship between expresser and observer. However, there is also evidence suggesting that it is a social cue regulating social interactions and that consequently mimicry varies as a function of social context and the type of emotion expression shown. Two studies were conducted to the assess impact of social group membership and type of expression on facial mimicry. Results suggest that the level of facial mimicry varies as a function of group membership. Moreover, mimicry levels were influenced by the kind of emotion displayed by the expresser. Although participants mimicked happiness displays regardless of the expresser's group membership, negative emotions were either not mimicked or only when shown by an ingroup member.     

Are facial expressions contagious in the Japanese?

Previous studies, mainly with Caucasian samples, have shown that facial expressions of emotion are contagious, a phenomenon known as facial mimicry. This study examined facial mimicry using a Japanese sample. Participants were shown a series of Japanese faces (from Matsumoto and Ekman, 1988) on a computer screen expressing "happiness", "sadness", "anger", or "disgust". While viewing the facial expressions, electoromyograms (EMG) of the participants' faces were recorded to see whether their own facial muscles corresponding to the stimulus faces were activated. Consistent with the previous studies using Caucasian samples, all four facial expressions were mimicked. The peak time of mimicry of angry or happy faces was later, while that of disgusted faces was relatively sooner. The potential relation of facial mimicry to "emotional contagion", a social phenomenon whereby subjective feelings transfer between people, is discussed.     

Steady State Visually Evoked Potential Correlates of Static and Dynamic Emotional Face Processing

While the neural regions associated with facial identity recognition are considered to be well defined, the neural correlates of non-moving and moving images of facial emotion processing are less clear. This study examined the brain electrical activity changes in 26 participants (14 males M = 21.64, SD = 3.99; 12 females M = 24.42, SD = 4.36), during a passive face viewing task, a scrambled face task and separate emotion and gender face discrimination tasks. The steady state visual evoked potential (SSVEP) was recorded from 64-electrode sites. Consistent with previous research, face related activity was evidenced at scalp regions over the parieto-temporal region approximately 170 ms after stimulus presentation. Results also identified different SSVEP spatio-temporal changes associated with the processing of static and dynamic facial emotions with respect to gender, with static stimuli predominately associated with an increase in inhibitory processing within the frontal region. Dynamic facial emotions were associated with changes in SSVEP response within the temporal region, which are proposed to index inhibitory processing. It is suggested that static images represent non-canonical stimuli which are processed via different mechanisms to their more ecologically valid dynamic counterparts.     

Sex differences in muscle fatigability and activation patterns of the human quadriceps femoris

The purposes of this study were to determine if the fatigability of the quadriceps femoris varies by biological sex under conditions of normal muscle blood flow and ischemia, and if differences in neuromuscular activation patterns exist. Young men and women (n=11/group; age 20–39 years) performed a sustained knee extension contraction at 25% of maximal force under conditions of occluded (OCC) and normal muscle blood flow (NON-OCC). Electromyographic (EMG) activity was recorded from the vastus lateralis (VL), rectus femoris (RF), vastus medialis (VM) and biceps femoris (BF) muscles, and analyzed for fatigue-induced changes in the amplitude and burst rate and duration (transient changes in motor unit recruitment) of the signal. Additionally, force fluctuations during the sustained contraction were quantified. Women had a longer time to task failure during the NON-OCC task [214.9±20.5 vs. 169.1±20.5 (SE) s] (P=0.02), but not during the OCC task (179.6+19.6 vs. 165.2±19.6 s). EMG data demonstrated sex differences in the neuromuscular activation pattern of the RF muscle and the collectively averaged QF muscles. During the NON-OCC and OCC tasks women achieved a higher relative activation of the RF at task failure than men (NON-OCC: 40.68±4.57 vs. 24.49±4.19%; OCC: 36.80±5.45 vs. 24.41±2.12%) (P=0.02 and 0.05, respectively). Also, during both tasks, they demonstrated a greater relative activation at task failure than men when an average of the VL, VM and RF was considered. Additionally, women exhibited a greater coefficient of variation in force fluctuations during the last-third of the fatiguing NON-OCC task (6.21±0.567 vs. 4.56±0.56%) (P=0.001). No sex differences in EMG burst rate or duration were observed, although there was a trend towards greater EMG burst rate of the RF in association with muscle fatigue in the women (P=0.09). Interestingly, the only neuromuscular activation variable that displayed a significant relationship with the time to task failure was the average relative EMG of the QF at task failure, and this relationship was observed under both experimental blood flow conditions (NON-OCC: r=0.47, P=0.03; OCC: r=0.44, P=0.04). These results indicate that sex differences in muscle blood flow and/or muscle metabolism are in part responsible for the female advantage in fatigue-resistance. Additionally, these findings suggest that men synergistically recruit the RF compartment to a lesser extent than women in association with muscle fatigue, and that women achieve an overall greater relative activation of the QF at task failure than men. However, the implications of these sex differences in neuromuscular activation patterns during fatiguing muscular contractions on the ability to withstand muscle fatigue (prolonged time to task failure) does not appear to be causally related.     

Recognition of Facial Expressions: Selective Impairment of Specific Emotions in Huntington's Disease

Recognition of facial expressions of basic emotions was investigated in HL and UJ, two people with Huntington's disease who showed little evidence of general cognitive deterioration. No impairments were found in tests of the perception of age, sex, familiar face identity, unfamiliar face identity, and gaze direction, indicating adequate processing of the face as a physical stimulus. Computer-interpolated ("morphed") images of facial expressions of basic emotions were used to demonstrate deficits in the recognition of disgust and fear for UJ. HL also showed a deficit in the recognition of disgust, and was not very adept (but not significantly impaired) at recognising fear. Other basic emotions (happiness, surprise, sadness, anger) were recognised atnormal levels of performance by HL and UJ. These results show that impairments of emotion recognition can be circumscribed; affecting some emotions more than others, and occurring in people who do not show pronounced perceptual or intellectual deterioration. Questionnaires examining self-assessed emotion indicated normal experience of anger by HL and UJ, but possible abnormalities for disgust and fear. The processes involved in recognising other people's emotions may therefore be linked to those involved in experiencing emotion, and the basic emotions of fear and disgust may have separable neural substrates.     

Task failure during standing heel raises is associated with increased power from 13 to 50 Hz in the activation of triceps surae

The goal of this paper was to investigate the amplitude and sub-100 Hz frequency content of surface electromyography (EMG) signals obtained from agonist, antagonist and synergist muscles during a heel-raise task sustained to failure. Twenty-two healthy adults, 14 men and 8 women participated in the study. Surface EMG data from the raising and lowering phases of the movement were studied in the time (EMG amplitude) and frequency (wavelet transform) domains. For the raising phase, we found a significant increase in the EMG amplitude of all muscles studied throughout the task (P < 0.02); however, for the lowering phase, we found a decrease in overall muscle activation for the medial gastrocnemius and tibialis anterior. Additionally, we found higher 13–30 and 30–50 Hz normalized power during the raising phase for the triceps surae prior to task failure and at task failure compared with the beginning and midway of the task (P < 0.05); during the lowering phase, however, we found higher normalized power from 30 to 50 Hz for the triceps surae (P < 0.01) and higher 13–30 Hz normalized power for the tibialis anterior (P < 0.01) at task failure compared with the beginning and midway of the task. Finally, we showed that a dynamic task performed until failure can induce different activation strategies for agonist, antagonist and synergist muscles, and that the frequency content below 100 Hz contains useful information about the neural activation of these muscles in relation to task failure that is not evident from the EMG amplitude.     

EMG feedback tasks reduce reflexive stiffness during force and position perturbations

Force and position perturbations are widely applied to identify muscular and reflexive contributions to posture maintenance of the arm. Both task instruction (force vs. position) and the inherently linked perturbation type (i.e., force perturbations-position task and position perturbations-force tasks) affect these contributions and their mutual balance. The goal of this study is to explore the modulation of muscular and reflexive contributions in shoulder muscles using EMG biofeedback. The EMG biofeedback provides a harmonized task instruction to facilitate the investigation of perturbation type effects irrespective of task instruction. External continuous force and position perturbations with a bandwidth of 0.5–20 Hz were applied at the hand while subjects maintained prescribed constant levels of muscular co-activation using visual feedback of an EMG biofeedback signal. Joint admittance and reflexive impedance were identified in the frequency domain, and parametric identification separated intrinsic muscular and reflexive feedback properties. In tests with EMG biofeedback, perturbation type (position and force) had no effect on joint admittance and reflexive impedance, indicating task as the dominant factor. A reduction in muscular and reflexive stiffness was observed when performing the EMG biofeedback task relative to the position task. Reflexive position feedback was effectively suppressed during the equivalent EMG biofeedback task, while velocity and acceleration feedback were both decreased by approximately 37%. This indicates that force perturbations with position tasks are a more effective paradigm to investigate complete dynamic motor control of the arm, while EMG tasks tend to reduce the reflexive contribution.     

Probing disrupted neurodevelopment in autism using human stem cell-derived neurons and organoids: An outlook into future diagnostics and drug development

Autism spectrum disorders (ASDs) represent a spectrum of neurodevelopmental disorders characterized by impaired social interaction, repetitive or restrictive behaviors, and problems with speech. According to a recent report by the Centers for Disease Control and Prevention, one in 68 children in the US is diagnosed with ASDs. Although ASD-related diagnostics and the knowledge of ASD-associated genetic abnormalities have improved in recent years, our understanding of the cellular and molecular pathways disrupted in ASD remains very limited. As a result, no specific therapies or medications are available for individuals with ASDs. In this review, we describe the neurodevelopmental processes that are likely affected in the brains of individuals with ASDs and discuss how patient-specific stem cell-derived neurons and organoids can be used for investigating these processes at the cellular and molecular levels. Finally, we propose a discovery pipeline to be used in the future for identifying the cellular and molecular deficits and developing novel personalized therapies for individuals with idiopathic ASDs.     

Time course of implicit processing and explicit processing of emotional faces and emotional words

Facial expressions are important emotional stimuli during social interactions. Symbolic emotional cues, such as affective words, also convey information regarding emotions that is relevant for social communication. Various studies have demonstrated fast decoding of emotions from words, as was shown for faces, whereas others report a rather delayed decoding of information about emotions from words. Here, we introduced an implicit (color naming) and explicit task (emotion judgment) with facial expressions and words, both containing information about emotions, to directly compare the time course of emotion processing using event-related potentials (ERP). The data show that only negative faces affected task performance, resulting in increased error rates compared to neutral faces. Presentation of emotional faces resulted in a modulation of the N170, the EPN and the LPP components and these modulations were found during both the explicit and implicit tasks. Emotional words only affected the EPN during the explicit task, but a task-independent effect on the LPP was revealed. Finally, emotional faces modulated source activity in the extrastriate cortex underlying the generation of the N170, EPN and LPP components. Emotional words led to a modulation of source activity corresponding to the EPN and LPP, but they also affected the N170 source on the right hemisphere. These data show that facial expressions affect earlier stages of emotion processing compared to emotional words, but the emotional value of words may have been detected at early stages of emotional processing in the visual cortex, as was indicated by the extrastriate source activity.