Relating alpha power modulations to competing visuospatial attention theories

Visuospatial attention theories often propose hemispheric asymmetries underlying the control of attention. In general support of these theories, previous EEG/MEG studies have shown that spatial attention is associated with hemispheric modulation of posterior alpha power (gating by inhibition). However, since measures of alpha power are typically expressed as lateralization scores, or collapsed across left and right attention shifts, the individual hemispheric contribution to the attentional control mechanism remains unclear. This is, however, the most crucial and decisive aspect in which the currently competing attention theories continue to disagree. To resolve this long-standing conflict, we derived predictions regarding alpha power modulations from Heilman's hemispatial theory and Kinsbourne's interhemispheric competition theory and tested them empirically in an EEG experiment. We used an attention paradigm capable of isolating alpha power modulation in two attentional states, namely attentional bias in a neutral cue condition and spatial orienting following directional cues. Differential alpha modulations were found for both hemispheres across conditions. When anticipating peripheral visual targets without preceding directional cues (neutral condition), posterior alpha power in the left hemisphere was generally lower and more strongly modulated than in the right hemisphere, in line with the interhemispheric competition theory. Intriguingly, however, while alpha power in the right hemisphere was modulated by both, cue-directed leftward and rightward attention shifts, the left hemisphere only showed modulations by rightward shifts of spatial attention, in line with the hemispatial theory. This suggests that the two theories may not be mutually exclusive, but rather apply to different attentional states

Prismatic adaptation modulates oscillatory EEG correlates of motor preparation but not visual attention in healthy participants

Prismatic adaption (PA) has been proposed as a tool to induce neural plasticity and is used to help neglect rehabilitation. It leads to a recalibration of visuo-motor coordination during pointing as well as to after-effects on a number of sensorimotor and attention tasks, but whether these effects originate at a motor or attentional level remains a matter of debate. Our aim was to further characterise PA after-effects by using an approach that allows distinguishing between effects on attentional and motor processes. We recorded electroencephalography (EEG) in healthy human participants (9 females and 7 males) while performing a new double step, anticipatory attention/motor preparation paradigm before and after adaptation to rightward shifting prisms, with neutral lenses as a control. We then examined PA after-effects through changes in known oscillatory EEG signatures of spatial attention orienting and motor preparation in the alpha and beta frequency bands. Our results were twofold. First, we found PA to rightward shifting prisms to selectively affect EEG signatures of motor but not attentional processes. More specifically, PA modulated preparatory motor EEG activity over central electrodes in the right hemisphere, contralateral to the PA-induced, compensatory leftward shift in pointing movements. No effects were found on EEG signatures of spatial attention orienting over occipito-parietal sites. Second, we found the PA effect on preparatory motor EEG activity to dominate in the beta frequency band. We conclude that changes to intentional visuo-motor rather than attentional visuo-spatial processes underlie the PA after-effect of rightward deviating prisms in healthy participants

Left parietal tACS at alpha frequency induces a shift of visuospatial attention

Background Voluntary shifts of visuospatial attention are associated with a lateralization of parieto-occipital alpha power (7-13Hz), i.e. higher power in the hemisphere ipsilateral and lower power contralateral to the locus of attention. Recent noninvasive neuromodulation studies demonstrated that alpha power can be experimentally increased using transcranial alternating current stimulation (tACS). Objective/Hypothesis We hypothesized that tACS at alpha frequency over the left parietal cortex induces shifts of attention to the left hemifield. However, spatial attention shifts not only occur voluntarily (endogenous/ top-down), but also stimulus-driven (exogenous/ bottom-up). To study the task-specificity of the potential effects of tACS on attentional processes, we administered three conceptually different spatial attention tasks. Methods 36 healthy volunteers were recruited from an academic environment. In two separate sessions, we applied either high-density tACS at 10Hz, or sham tACS, for 35–40 minutes to their left parietal cortex. We systematically compared performance on endogenous attention, exogenous attention, and stimulus detection tasks. Results In the endogenous attention task, a greater leftward bias in reaction times was induced during left parietal 10Hz tACS as compared to sham. There were no stimulation effects in either the exogenous attention or the stimulus detection task. Conclusion The study demonstrates that high-density tACS at 10Hz can be used to modulate visuospatial attention performance. The tACS effect is task-specific, indicating that not all forms of attention are equally susceptible to the stimulation

Parkinson's disease dementia: a neural networks perspective.

In the long-term, with progression of the illness, Parkinson's disease dementia affects up to 90% of patients with Parkinson's disease. With increasing life expectancy in western countries, Parkinson's disease dementia is set to become even more prevalent in the future. However, current treatments only give modest symptomatic benefit at best. New treatments are slow in development because unlike the pathological processes underlying the motor deficits of Parkinson's disease, the neural mechanisms underlying the dementing process and its associated cognitive deficits are still poorly understood. Recent insights from neuroscience research have begun to unravel the heterogeneous involvement of several distinct neural networks underlying the cognitive deficits in Parkinson's disease dementia, and their modulation by both dopaminergic and non-dopaminergic transmitter systems in the brain. In this review we collate emerging evidence regarding these distinct brain networks to give a novel perspective on the pathological mechanisms underlying Parkinson's disease dementia, and discuss how this may offer new therapeutic opportunities

Automatic visuospatial attention shifts: Perceptual correlates, interventions and oscillatory signatures

Our visual perception is shaped by both external and internal factors, which continuously compete for limited neural resources. Salient external (exogenous) events capture our attention automatically, whereas internal (endogenous) attention can be directed towards sensory events according to our current behavioural goals. Advances in neuroimaging and brain stimulation have allowed us to begin to map the underlying functional neural architecture mediating both exogenously driven and endogenously controlled visual attention, including electrophysiological techniques such as electroencephalography and magnetoencephalography (EEG/MEG). However, while the neural EEG/MEG correlates of endogenously controlled attention have been investigated in much detail, the neural EEG/MEG correlates of exogenously driven attention are substantially less well understood. One reason for this is that exogenously driven effects are difficult to isolate from the influence of endogenous control processes. In a series of three experiments, I sought to: 1) Study how the perceptual outcomes of both endogenously and exogenously driven attention can be effectively dissociated and investigated. 2) Provide a better understanding of the functional architecture of attention control in regards to its underlying neural substrates and oscillatory signatures, particularly when exogenously driven. To this end, I employed a visuospatial attention paradigm which, by design, behaviourally dissociates exogenous from endogenously driven effects (experiment 1). Furthermore, by utilizing the same behavioural paradigm in combination with neuronavigated MRI-based transcranial magnetic stimulation (TMS) over two key attentional network nodes (i.e., the right intraprarietal sulcus and right temporo-parietal junction), I probed the extent to which the neural substrates of endogenous vs. exogenous orienting are overlapping or can be dissociated (experiment 2). Lastly, I used electroencephalography (EEG) to investigate the oscillatory signatures underlying attention in a task which is typically employed to study exogenous orienting and which putatively triggers exogenous attention in isolation (experiment 3). The results revealed that while exogenous attentional processes can be behaviourally dissociated from endogenous attention (experiment 1), the neural substrates of exogenous attention appear to cover a wide network of attention areas. This includes nodes in both the right ventral attention network (i.e., right temporo-parietal junction) but also the right dorsal network (i.e., the right intraparietal sulcus), which has predominantly been associated with endogenous attention control (experiment 2). Interestingly, even in tasks that have been utilized to test exogenous attentional effects in isolation, endogenous control processes, as indexed by increased mid-frontal theta-band activity, can heavily influence the behavioural outcome (experiment 3). Based on these results, I conclude that there appears to be strong interplay between endogenous control and exogenously driven attention processes. These findings highlight that in order to better understand the functional architecture of (purely) exogenously driven effects, we need to effectively account for the potential influence of endogenous control. One approach to achieve this is by manipulating both types of attention simultaneously instead of in separation, as illustrated in the present work

New insights on the ventral attention network::active suppression and involuntary recruitment during a bimodal task

International audienceDetection of unexpected, yet relevant events is essential in daily life. fMRI studies have revealed the involvement of the ventral attention network (VAN), including the temporo-parietal junction (TPJ), in such process. In this MEG study with 34 participants (17 women), we used a bimodal (visual/auditory) attention task to determine the neuronal dynamics associated with suppression of the activity of the VAN during top-down attention and its recruitment when information from the unattended sensory modality is involuntarily integrated. We observed an anticipatory power increase of alpha/beta oscillations (12–20 Hz, previously associated with functional inhibition) in the VAN following a cue indicating the modality to attend. Stronger VAN power increases were associated with better task performance, suggesting that the VAN suppression prevents shifting attention to distractors. Moreover, the TPJ was synchronized with the frontal eye field in that frequency band, indicating that the dorsal attention network (DAN) might participate in such suppression. Furthermore, we found a 12–20 Hz power decrease and enhanced synchronization, in both the VAN and DAN, when information between sensory modalities was congruent, suggesting an involvement of these networks when attention is involuntarily enhanced due to multisensory integration. Our results show that effective multimodal attentional allocation includes the modulation of the VAN and DAN through upper-alpha/beta oscillations. Altogether these results indicate that the suppressing role of alpha/beta oscillations might operate beyond sensory regions

Dissociable Influences of Auditory Object vs. Spatial Attention on Visual System Oscillatory Activity

Given that both auditory and visual systems have anatomically separate object identification (“what”) and spatial (“where”) pathways, it is of interest whether attention-driven cross-sensory modulations occur separately within these feature domains. Here, we investigated how auditory “what” vs. “where” attention tasks modulate activity in visual pathways using cortically constrained source estimates of magnetoencephalograpic (MEG) oscillatory activity. In the absence of visual stimuli or tasks, subjects were presented with a sequence of auditory-stimulus pairs and instructed to selectively attend to phonetic (“what”) vs. spatial (“where”) aspects of these sounds, or to listen passively. To investigate sustained modulatory effects, oscillatory power was estimated from time periods between sound-pair presentations. In comparison to attention to sound locations, phonetic auditory attention was associated with stronger alpha (7–13 Hz) power in several visual areas (primary visual cortex; lingual, fusiform, and inferior temporal gyri, lateral occipital cortex), as well as in higher-order visual/multisensory areas including lateral/medial parietal and retrosplenial cortices. Region-of-interest (ROI) analyses of dynamic changes, from which the sustained effects had been removed, suggested further power increases during Attend Phoneme vs. Location centered at the alpha range 400–600 ms after the onset of second sound of each stimulus pair. These results suggest distinct modulations of visual system oscillatory activity during auditory attention to sound object identity (“what”) vs. sound location (“where”). The alpha modulations could be interpreted to reflect enhanced crossmodal inhibition of feature-specific visual pathways and adjacent audiovisual association areas during “what” vs. “where” auditory attention

Altered Alpha Oscillatory Power Dynamics Underlie Difficulties with Cognitive Flexibility

Cognitive flexibility is an important mental faculty, but there are certain populations that experience reduced flexibility, which may be associated with altered neural activity. Rumination is when an individual becomes mentally stuck on a thought, and they experience difficulty shifting their attention away from the ruminative thought demonstrating reduced cognitive flexibility. In a similar manner, individuals diagnosed with substance use disorder show varying degrees of attentional bias towards drug related stimuli. The drug cues capture attention, and it is difficult for these individuals to shift attention away from thoughts related to drug cues. Both populations experience difficulty shifting attention when they experience highly salient thoughts (high automatic constraints). Here we suggest and demonstrate that reduced cognitive flexibility in these populations is associated with altered activity of alpha oscillations, as alpha oscillations play an important role in supporting cognitive flexibility. In our first study, we assess the relationship between trait tendency to ruminate and resting state alpha power in left frontal and parietal located electrodes. Individuals higher in trait rumination exhibit higher alpha power in left frontal located electrodes. This finding suggests that higher alpha power may contribute to mental inflexibility associated with rumination. In our second study, we assess the relationship between attentional bias towards drug cues and alpha power while automatic constraints on thought are high during an emotional version of the Stroop task and when drug cues are not present and therefore automatic constraints are low, but flexibility is required during a probabilistic reversal learning task. The emotional version of the Stroop task includes traditional congruent and incongruent word meanings as well as drug related and neutral word meanings. Participants in this study were long-term nicotine smokers, therefore the emotional stimuli were smoking related. The probabilistic reversal learning task instructs participants to choose one of two presented stimuli on each trial. The stimuli have different probabilities of reward or punishment. If the participant chooses the stimulus with the higher probability of reward several trials in a row, the reward probabilities reverse, and the participant must adapt to the new reward contingencies. Participants demonstrate the traditional Stroop effect of lower accuracy and slower reaction time during incongruent trials compared to congruent trials. Additionally, participants show a slowed reaction time during drug trials compared to neutral trials suggesting attentional bias during drug trials. Greater attentional bias is associated with higher alpha power in left frontal electrodes during drug trials. No significant relationship between attentional bias and alpha power during the probabilistic reversal learning task was revealed. Together, these results suggest higher alpha power in left frontal regions may contribute to mental inflexibility prompted by attentional bias when automatic constraints are high, but when automatic constraints are low, flexibility may not be reduced. All together these results reveal a relationship between reduced cognitive flexibility when salient stimuli or thoughts are present and altered alpha power dynamics, which may offer new avenues for behavioral intervention to improve cognitive flexibility

Actividad oscilatoria neuronal asociada con la orientación de la atención hacia las representaciones mentales de la memoria operativa

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Psicología, Departamento de Psicología Biológica y de la Salud. Fecha de lectura: 16-10-2015Selective attention mechanisms allow us to focus on information that is relevant to the current behavior and, equally important, ignore irrelevant information. Neural synchrony has been proposed to be a key mechanism underlying selective attention. Several models postulate that gamma and alpha band oscillations play a pivotal role in top-down processes such as selective attention, with antagonist roles. Whereas gamma synchronization is associated to processing of information; alpha synchronization has been associated with the functional inhibition of task-irrelevant regions. Recent studies have shown that, in the same way that attention can be selectively oriented to bias sensory processing in favor of relevant stimuli in perceptual tasks, it is also possible to retrospectively orient attention to internal representations held in working memory. However, these studies have not explored the associated oscillatory phenomena. In the present dissertation we explored the patterns of oscillatory activity associated to retrospectively orienting attention under the hypothesis that modulation of oscillatory activity is a general mechanism resulting from deployment of attention to the perceptual and mnemonic domains. MEG activity was recorded while participants performed a retro-cue change detection task. Participants benefited from retro-cues in terms of accuracy and reaction time. Lateralized gamma and alpha activity were found in occipital cortex. Gamma power was more pronounced in the ventral occipital cortex contralateral to the attended hemifield. While alpha was more strongly suppressed in the contralateral occipital cortex at the beginning of the delay period, it increased at the end of the retention in the ipsilateral occipital cortex. A subsequent behavioral experiment revealed that when participants cannot anticipate the probe location, the retro-cue is still beneficial, and thus, the benefit of retro-cue is not only due to anticipatory attentional mechanisms. An EEG experiment further found lateralized alpha activity in the absence of preparatory attention. These findings suggest that the oscillatory mechanisms underlying attentional orienting to representations held in working memory are similar to those engaged when attention is oriented in the perceptual spac