Santiago Galdo-Álvarez

The Emotional Movie Database (EMDB): A Self-Report and Psychophysiological Study

Film clips are an important tool for evoking emotional responses in the laboratory. When compared with other emotionally potent visual stimuli (e.g., pictures), film clips seem to be more effective in eliciting emotions for longer periods of time at both the subjective and physiological levels. The main objective of the present study was to develop a new database of affective film clips without auditory content, based on a dimensional approach to emotional stimuli (valence, arousal and dominance). The study had three different phases: (1) the pre-selection and editing of 52 film clips (2) the self-report rating of these film clips by a sample of 113 participants and (3) psychophysiological assessment [skin conductance level (SCL) and the heart rate (HR)] on 32 volunteers. Film clips from different categories were selected to elicit emotional states from different quadrants of affective space. The results also showed that sustained exposure to the affective film clips resulted in a pattern of a SCL increase and HR deceleration in high arousal conditions (i.e., horror and erotic conditions). The resulting emotional movie database can reliably be used in research requiring the presentation of non-auditory film clips with different ratings of valence, arousal and dominance.

Affective picture modulation: Valence, arousal, attention allocation and motivational significance

The present study analyses the modulatory effects of affective pictures in the early posterior negativity (EPN), the late positive potential (LPP) and the human startle response on both the peripheral (eye blink EMG) and central neurophysiological levels (Probe P3), during passive affective pictures viewing. The affective pictures categories were balanced in terms of valence (pleasant; unpleasant) and arousal (high; low). The data shows that EPN may be sensitive to specific stimulus characteristics (affective relevant pictures versus neutral pictures) associated with early stages of attentional processing. In later stages, the heightened attentional resource allocation as well as the motivated significance of the affective stimuli was found to elicit enhanced amplitudes of slow wave processes thought to be related to enhanced encoding, namely LPP,. Although pleasant low arousing pictures were effective in engaging the resources involved in the slow wave processes, the highly arousing affective stimuli (pleasant and unpleasant) were found to produce the largest enhancement of the LPP, suggesting that high arousing stimuli may are associated with increased motivational significance. Additionally the response to high arousing stimuli may be suggestive of increased motivational attention, given the heightened attentional allocation, as expressed in the P3 probe, especially for the pleasant pictures. The hedonic valence may then serve as a mediator of the attentional inhibition to the affective priming, potentiating or inhibiting a shift towards defensive activation, as measured by the startle reflex.

ERP evidence of MI activation without motor response execution

There has been controversy concerning the activity of the primary motor cortex (MI) during the mental rehearsal of movement (motor imagination). In this study we found that the lateralized readiness potential (LRP), an event-related potential probably generated in MI, appeared with similar latencies during both trials requiring execution of hand movements and trials requiring only their mental rehearsal, regardless of whether misleading pre-cues that increased latency were employed. However, LRPs obtained during imagination trials had smaller amplitudes. We conclude that MI is involved in motor imagination as well as in preparing overt movement, and that in overt movement the LRP sums neural activity common to these two situations and neural activity exclusive to overt movement.

Age-related changes in ERP correlates of visuospatial and motor processes.

Although previous ERP studies have demonstrated slowing of visuospatial and motor processes with age, such studies frequently included only young and elderly participants, and lacked information about age-related changes across the adult lifespan. The present research used a Simon task with two irrelevant dimensions (position and direction of an arrow) to study visuospatial (N2 posterior contralateral, N2pc) and motor (response-locked lateralized readiness potential, LRP-r) processes in young, middle-aged, and elderly adults. The reaction time and motor execution stage (LRP-r) increased gradually with age, while visuospatial processes (N2pc latency) were similarly delayed in the older groups. No age-related increase in interference was observed, probably related to a delay in processing the symbolic meaning of the direction in older groups, which was consistent with age-related differences in distributional analyses and N2pc amplitude modulations.

The Simon effect modulates N2cc and LRP but not the N2pc component.

Previous studies have reported that the horizontal arrangement of the stimuli in Simon tasks elicits three different components: LRP, N2pc and N2cc. Although N2cc may play a key role in Simon tasks, as it is involved in preventing responses based on stimulus position, modulation of the N2cc component according to the experimental conditions has not previously been investigated because of N2cc/LRP overlap in similar regions and temporal window. The aim of the present study was to investigate how the Simon effect modulates N2pc, N2cc and LRP components. For this purpose, participants were asked to respond to an arrow according to its colour. Three conditions, which depended on the congruency between stimulus position and the required response, were analysed: compatible position (CP), incompatible position (IP), and neutral position (NP). The LRP peak latency was delayed in IP with respect to CP and NP conditions. Lateralized minus neutral position (L-NP) subtractions were carried out to remove the common motor activity and isolate the N2cc and N2pc components in the lateralized conditions. The N2cc amplitude in L-NP waveforms was larger in IP than in CP, in accordance with the greater effort required to monitor selection of the correct response in the first condition. eLORETA analysis also revealed greater premotor activity at 150-200 ms in IP and CP, than in NP, which was attributed to the N2cc component present in IP/CP conditions. Evidence of functional dissociation between N2pc and N2cc components was obtained, because N2cc, but not N2pc, was affected by the experimental conditions.

Electrophysiological Correlates of Amnestic Mild Cognitive Impairment in a Simon Task

Amnestic mild cognitive impairment (aMCI) represents a prodromal stage of Alzheimer`s disease (AD), especially when additional cognitive domains are affected (Petersen et al., 2009). Thus, single-domain amnestic MCI (sdaMCI) and multiple-domain-amnestic MCI (mdaMCI) biomarkers are important for enabling early interventions to help slow down progression of the disease. Recording event-related potentials (ERPs) is a non-invasive and inexpensive measure of brain activity associated with cognitive processes, and it is of interest from a clinical point of view. The ERP technique may also be useful for obtaining early sdaMCI and mdaMCI biomarkers because ERPs are sensitive to impairment in processes that are not manifested at behavioral or clinical levels. In the present study, EEG activity was recorded in 25 healthy participants and 30 amnestic MCI patients (17 sdaMCI and 13 mdaMCI) while they performed a Simon task. The ERPs associated with visuospatial (N2 posterior-contralateral – N2pc -) and motor (lateralized readiness potential – LRP –) processes were examined. The N2pc amplitude was smaller in participants with mdaMCI than in healthy participants, which indicated a decline in the correlates of allocation of attentional resources to the target stimulus. In addition, N2pc amplitude proved to be a moderately good biomarker of mdaMCI subtype (0.77 sensitivity, 0.76 specificity). However, the LRP amplitude was smaller in the two MCI groups (sdaMCI and mdaMCI) than in healthy participants, revealing a reduction in the motor resources available to execute the response in sdaMCI and mdaMCI patients. Furthermore, the LRP amplitude proved to be a valid biomarker (0.80 sensitivity, 0.92 specificity) of both amnestic MCI subtypes.

Electrophysiological correlates of semantic processing in Williams syndrome

Williams syndrome (WS), a genetic neurodevelopmental disorder due to microdeletion in chromosome 7, has been described as a syndrome with an intriguing socio-cognitive phenotype. Cognitively, the relative preservation of language and face processing abilities coexists with severe deficits in visual-spatial tasks, as well as in tasks involving abstract reasoning. However, in spite of early claims of the independence of language from general cognition in WS, a detailed investigation of language subcomponents has demonstrated several abnormalities in lexical-semantic processing. Nonetheless, the neurobiological processes underlying language processing in Williams syndrome remain to be clarified. The aim of this study was to examine the electrophysiological correlates of semantic processing in WS, taking typical development as a reference. A group of 12 individuals diagnosed with Williams syndrome, with age range between 9 and 31 years, was compared with a group of typically developing participants, individually matched in chronological age, gender and handedness. Participants were presented with sentences that ended with words incongruent (50%) with the previous sentence context or with words judged to be its best completion (50%), and they were asked to decide if the sentence made sense or not. Results in WS suggest atypical sensory ERP components (N100 and P200), preserved N400 amplitude, and abnormal P600 in WS, with the latter being related to late integration and re-analysis processes. These results may represent a physiological signature of underlying impaired on-line language processing in this disorder.

Differences between Mild Cognitive Impairment Subtypes as Indicated by Event-Related Potential Correlates of Cognitive and Motor Processes in a Simon Task

Mild cognitive impairment (MCI) may represent a prodromal stage of Alzheimers disease (AD), although the clinical manifestations of MCI are heterogeneous. Consequently, MCI subtypes are differentiated since amnestic decline (particularly when combined with decline on multiple cognitive domains) increases the probability of progression to AD. In the present study, event-related potential (ERP) correlates of stimulus evaluation (N2), visuospatial attention (negativity posterior-contralateral, N2pc), stimulus categorization (P3b), executive control (pre-response positivity, PP, and medial frontal negativity), and motor (lateralized readiness potential, LRP) processes were studied in 53 participants while they performed a Simon task. Participants were divided into control group (CG), multiple-domain non-amnestic MCI (mdnaMCI), single-domain amnestic MCI (sdaMCI), and multiple-domain amnesic MCI (mdaMCI). Although there were no differences in reaction times and percentage of errors in the performed Simon-type task, a differential pattern of electrophysiological correlates was observed in MCI compared to CG. Concretely, amnestic MCI (sdaMCI and mdaMCI) showed reduced motor activity (LRP amplitude; AUC: 0.84); impairment in executive control (PP amplitude; AUC: 0.80) was observed in multiple-domain MCI (mdaMCI and mdnaMCI); finally, stimulus evaluation (N2 latency; AUC: 0.86) and visuospatial attention (N2pc amplitude; AUC: 0.78) was affected in mdaMCI. Overall, results linked the poorer prognosis of the mdaMCI subtype with a greater number of differences in ERP correlates regarding CG. Therefore, the present results enable us to suggest possible ERP biomarkers for specific MCI subtypes.

Age-related effects on event-related brain potentials in a congruence/incongruence judgment color-word Stroop task

We examined the event-related brain potentials elicited by color-word stimuli in a Stroop task in which healthy participants (young and old) had to judge whether the meaning and the color of the stimulus were congruent or incongruent. The Stroop effect occurred in both age groups, with longer reaction times in the older group than in the young group for both types of stimuli, but no difference in the number of errors made by either group. Although the N2 and P3b latencies were longer in the older than in the younger group, there were no differences between groups in the latencies of earlier event-related potential components, and therefore the age-related processing slowing is not generalized. The frontal P150 amplitude was larger, and the parietal P3b amplitude was smaller, in the older than in the younger group. Furthermore, the P3b amplitude was maximal at frontal locations in older participants and at parietal locations in young participants. The age-related increase in perceptual resources and the posterior-to-anterior shift in older adults support adaptive reorganization of the neural networks involved in the processing of this Stroop-type task.

Age-related prefrontal over-recruitment in semantic memory retrieval: Evidence from successful face naming and the tip-of-the-tongue state.

Studies that have attempted to determine the effects of aging on the brain neural sources of memory retrieval have reported two contrasting age effects: under-recruitment and over-recruitment of several prefrontal areas. However, the causes for these effects are still a matter of debate. In order to study the underlying factors that cause the effects, we compared brain activation in young and older adults, in a successful word retrieval condition, and a failed word retrieval condition: the tip-of-the-tongue state. For this, we used the event-related potentials technique and neural source estimation with low-resolution tomographies. The results showed that the older adults did not display under-recruitment in any brain area in comparison with the young adults. However, they displayed additional prefrontal activation that varied depending on the processing stage and the condition, which supports the hypothesis of selective over-recruitment in older adults.