Noninvasive brain stimulation techniques can modulate cognitive processing

Recent methods that allow a noninvasive modulation of brain activity are able to modulate human cognitive behavior. Among these methods are transcranial electric stimulation and transcranial magnetic stimulation that both come in multiple variants. A property of both types of brain stimulation is that they modulate brain activity and in turn modulate cognitive behavior. Here, we describe the methods with their assumed neural mechanisms for readers from the economic and social sciences and little prior knowledge of these techniques. Our emphasis is on available protocols and experimental parameters to choose from when designing a study. We also review a selection of recent studies that have successfully applied them in the respective field. We provide short pointers to limitations that need to be considered and refer to the relevant papers where appropriate

rTMS evidence for a dissociation in short-term memory for spoken words and nonwords

Differing patterns of verbal short-term memory (STM) impairment have provided unique insights into the relationship between STM and broader language function. Lexicality effects (i.e., better recall for words than nonwords) are larger in patients with phonological deficits following left temporoparietal lesions, and smaller in patients with semantic impairment and anterior temporal damage, supporting linguistic accounts of STM. However, interpretation of these patient dissociations are complicated by (i) non-focal damage and (ii) confounding factors and secondary impairments. This study addressed these issues by examining the impact of inhibitory transcranial magnetic stimulation (TMS) on auditory-verbal STM performance in healthy individuals. We compared the effects of TMS to left anterior supramarginal gyrus (SMG) and left anterior middle temporal gyrus (ATL) on STM for lists of nonwords and random words. SMG stimulation disrupted nonword recall, in a pattern analogous to that observed in patients, compatible with a role for this site in processing speech sounds without support from long-term lexical-semantic representations. Stimulation of ATL, a semantic site, disrupted the recall of words but not nonwords. A visual pattern memory task indicated that these effects of TMS were restricted to the verbal domain. These data provide convergent evidence for the conclusions of neuropsychological studies that support linguistic accounts of verbal STM

Scalar Short-Term Memory

The location of the brain’s working and short-term memory (WM/STM) “system” is unclear. The existence of a dedicated WM/STM system is itself under debate. Recently, it has been proposed that WM/STM storage relies not on a dedicated system in prefrontal cortex, but rather that it is an emergent function of interaction between attentional and representational systems (e.g., sensory cortex) in the brain. However, mnemonic representations of very simple stimuli have repeatedly been shown to exist in frontal cortex. In this manuscript, I use computational and behavioural methods to demonstrate similarities between the representations of different types of very simple stimuli in memory, and argue that this is evidence that present theory must be extended to deal with current experimental results

Verbal short-term memory and vocabulary learning

This thesis addressed two key issues. The first was the extent to which verbal short-term memory (STM) for item and order information can be differentiated in terms of their underlying neural mechanisms. The second was to analyze the relative contributions of item and order STM to vocabulary learning in bilingual (BL) and monolingual (ML) children and ML adults. The first issue was addressed with four studies. Three used electroencephalography (EEG) with ML adults, BL adults and ML children. The aim was to determine whether there is any evidence that the two types of verbal STM have different neural signatures. The fourth study used transcranial magnetic stimulation (TMS) in ML adults to test the hypothesis that the right intraparietal sulcus (IPS) is involved in order STM but not item STM. The second issue was addressed by two behavioural studies. The first was a large-scale longitudinal study testing item and order STM in relation to natural vocabulary acquisition in 7 to 10 year old BL and ML children. The children were tested once in the beginning and once in the end of the school year. In addition, ML children learning a second language were examined in the end of the school year. The second behavioural study explored therelationship of item and order STM with new-word-learning in ML adults using artificially-created nonwords. Some evidence was found to support the view that the distinction of item and order STM is a useful one. Results of the EEG data suggested differences in patterns of neuro-electrical activity for ML and BL adults and ML children when they are performing item STM and order STM tasks. The results suggest that order STM is important for new word learning in one´s native language learning, where there has already been some exposure to this language, but not in complete novice language learners

Closed-loop photic stimulation using EEG

Accumulating evidence indicates that neural oscillations play a central role in brain function, organising and modulating brain activity in response to both bottom-up exogenous stimuli and top-down endogenous dynamics. It has been pointed out that abnormalities in oscillatory dynamics are sometimes associated with various neuropathologies. Consequently, it has been posited that normalising pathological oscillations in these conditions may reduce negative symptoms of brain disorders. One potential technique for this is photic brain stimulation. However, while it has been shown to be able to increase the power of targeted frequency bands during stimulation, it remains an open question as to whether it is possible to also suppress the amplitude of a frequency band by rhythmic light stimulation. In this thesis, we will explore different light stimulation protocols, assessing whether a more general control of the alpha frequency band is possible. Specifically, we are exploring the during- and post-stimulation impact of photic stimulation and the feasibility that closed-loop interaction between high-luminance LEDs and an electroencephalography (EEG) brain activity signal can both increase and decrease alpha frequency power across the visual cortex while stimulation is being applied

How the brains of young and old human adults cope with increased working memory demands

Working memory tasks are generally more difficult for older adults due to decreasing working memory capacity that is evoked by changes in the ageing brain. To successfully cope with this increased challenge in cognitive demand, elderly adults additionally activate the contralateral counterparts of specific prefrontal brain regions, whereas young adults do engage them unilaterally. At first glance, this strategy seems at odds with the idea of lateralized cognitive functions in cerebral cortex. In this dissertation, I investigated whether bilateral recruitment is a general strategy of the human brain to respond to increased working memory demands that is independent of age, task content and cerebral region. To answer these questions, we conducted our main experiment in which a group of young and a group of old adult participants worked on verbal, spatial, and object-based working memory tasks that had been individually tailored to push each subject to her or his capacity limit in each working memory domain. Simultaneously, we used functional magnetic resonance imaging to measure brain activity associated with working memory maintenance and to compare this activity between cross-hemispheric counterparts of the respective brain regions. Our results clearly indicate that language-related regions such as Broca’s area in the left ventrolateral prefrontal cortex, the left supplementary motor area, right lobule VI and crus1 of lobule VII of the cerebellum, and the left ventral premotor cortex maintained their lateralized activation patterns across the two age groups despite our highly challenging working memory tasks. In contrast, dorsolateral prefrontal cortex and anterior prefrontal cortex showed bilateral activation in difficult conditions across all working memory domains and this was true for both age groups. To further confirm that also young adults shift from a unilateral to a bilateral recruitment of these prefrontal brain regions in easy vs. highly demanding working memory tasks, respectively, we conducted an additional control experiment that engaged both the verbal and the spatial working memory domain. The results of this control experiment demonstrated that dorsolateral prefrontal cortex and anterior prefrontal cortex are unilaterally recruited during the easy task variants and – together with the results of the main experiment – they showed that this unilaterality transforms into bilaterality in difficult tasks. The additional activation of contralateral cerebral counterparts seems to be a strategy of the brain to cope with increased cognitive challenges independent of age and working memory task content. This phenomenon mainly emerges in prefrontal cortex – a brain structure that is less specialized and more flexible than other parts of the brain

Neural mechanisms of temporal resolution of attention

The dynamic nature of the world requires that our visual representations are continuously updated. These representations are more precise if there is a narrow time window over which information is averaged. We assess the neural processes of visual updating by testing patients with lesions including inferior parietal cortex, control patients and healthy adults on a continuous visual monitoring task. In Experiment 1, observers kept track of the changing spatial period of a luminance grating and identified the final spatial period after the stimulus disappeared. Healthy older adults and neurological controls were able to perform better than simulated guesses, but only 3 of 11 patients with damage including parietal cortex were able to reach performance that differed from simulated guesses. The effects were unrelated to lesion size. Poor performance on this task is consistent with an inability to selectively attend to the final moment at which the stimulus was seen. To investigate the temporal limits of attention, we varied the rate of stimulus change in Experiment 2. Performance remained poor for some patients even with slow 2.5 Hz change rates. The performance of 4 patients with parietal damage displayed poor temporal precision, namely recovery of performance with slower rates of change

Long-term memory encoding of facial information in humans: an EEG and tACS study

In recent years, the investigation of memory formation and retrieval has attracted increasing interest. As oscillatory activity plays a crucial role in neuroplastic processes, episodic memory is to a considerable extent attributable to synaptic changes, synchronization, and neurophysiological alterations through oscillating electric fields. Perception processes are part of episodic memory encoding. Human face perception and encoding arouse particular interest due to their fundamental relevance in social behavior. This study aimed to determine the causal role of brain dynamics in the encoding of facial episodic memory in humans. As recent studies revealed an enhancement in cognitive processes by the entrainment of internal brain oscillations, tACS stepped up as a new method of non-invasive brain stimulation to induce neuroplasticity (Antal et al. 2008; Antal and Herrmann 2016). It is a promising tool to test the role of brain oscillations on episodic memory encoding in humans and the potential for memory improvement. For the entire study, we developed a memory task that includes encoding, a Short-Term Memory Retrieval Part, maintenance, and a Long-Term Memory Retrieval Part. In the longterm face recognition, we assessed both the performance and the choice confidence on the 3-point scale. Two consecutive experiments were performed. For the first experiment (20 participants), we used 128-channel EEG to identify the region of the brain that is exclusively responsible for the long-term face encoding and the frequency of the brain rhythm that is associated with the successful subsequent recognition. Then, we conducted the tACS experiment (25 participants) based on the frequency and spatial data from the EEG experiment. We implemented a double-blinded, randomized, counterbalanced, crossover, and placebo-controlled study design. 20 minutes of 4 Hz-tACS at 3 mA peak-to-peak were applied during the encoding task to the identified right or to the left TPO area for active control. One more session included sham stimulation to one or the other area. The EEG study revealed a significant synchronization of brain oscillations during successful long-term facial memory encoding in the right TPO area at the low theta range (4 Hz). In complete agreement, the placebo-controlled tACS study showed a significant enhancement of long-term memory recognition performance after the low theta-stimulation of the right but not the left TPO area. The results indicate that low theta oscillations in the right TPO area are vital for successful episodic long-term memory encoding of facial stimuli. Secondly, we confirm that active low theta-tACS applied on this area during encoding improves the subsequent memory recognition performance. This supports the concept of lateralization for face processing in the right posterior brain region; moreover it puts forward this area as a crucial neocortical node in communication with the hippocampus for the long-term memory encoding (Pitcher et al. 2011; Geib et al. 2017). The results are in agreement with other studies that revealed a positive correlation between theta power and memory performance (Pahor and Jaušovec 2014; Clouter et al. 2017). However, the present work reveals a causal link between the empowered low theta in the right TPO area and enhanced subsequent long-term memory recognition. In summary, tACS is a highly suitable non-invasive tool to entrain local neocortical low theta activity and enhance long-term memory encoding, which is important in the clinical context for revealing novel therapeutic strategies in prosopagnosia and prosopamnesia.2021-09-1

TMS application in both health and disease

Transcranial magnetic stimulation (TMS) can be useful for therapeutic purposes for a variety of clinical conditions. Numerous studies have indicated the potential of this noninvasive brain stimulation technique to recover brain function and to study physiological mechanisms. Following this line, the articles contemplated in this Research Topic show that this field of knowledge is rapidly expanding and considerable advances have been made in the last few years. There are clinical protocols already approved for Depression (and anxiety comorbid with major depressive disorder), Obsessive compulsive Disorder (OCD), migraine headache with aura, and smoking cessation treatment but many studies are concentrating their efforts on extending its application to other diseases, e.g., as a treatment adjuvant. In this Research Topic we have the example of using TMS for pain, post-stroke depression, or smoking cessation, but other diseases/injuries of the central nervous system need attention (e.g., tinnitus or the surprising epilepsy). Further, the potential of TMS in health is being explored, in particular regarding memory enhancement or the mapping of motor control regions, which might also have implications for several diseases. TMS is a non-invasive brain stimulation technique that can be used for modulating brain activation or to study connectivity between brain regions. It has proven efficacy against neurological and neuropsychiatric illnesses but the response to this stimulation is still highly variable. Research works devoted to studying the response variability to TMS, as well as large-scale studies demonstrating its efficacy in different sub-populations, are therefore of utmost importance. In this editorial, we summarize the main findings and viewpoints detailed within each of the 12 contributing articles using TMS for health and/or disease applications.publishe

Short-term memory of temporal aspects of noxious and innocuous thermal sensation : psychophysical and fMRI studies

La douleur peut être considérée comme un système de protection qui signale une menace et qui nous avertit des dégâts imminents aux tissus. En tant que mécanisme de défense, il nécessite l'apprentissage et la mémoire des expériences du passé pour la survie et les comportements liés à la douleur. Par conséquent, notre expérience de la douleur actuelle est fortement influencée par les expériences antérieures et l'apprentissage. Cependant, malgré son importance, notre compréhension actuelle de l'interaction entre le système de la douleur et le système de mémoire est très limitée. La mémoire de la douleur est un sujet de recherche très vaste. Il nécessite une compréhension des mécanismes impliqués à chaque étape du système de mémoire (mémoire immédiate, à court terme et à long terme) et l'interaction entre eux. Parmi les étapes multiples de la mémoire, la mémoire à court terme de la douleur est une zone qui est moins recherchée, alors qu'il existe une énorme quantité de recherche neuroscientifique dans la mémoire à court terme sur d'autres modalités, en particulier la vision. L'étude de la mémoire à court terme de la douleur est particulièrement importante car cette trace de la mémoire à court terme de la douleur est ensuite convertie en mémoire à long terme et affecte ensuite les expériences futures de la douleur. Cette thèse est largement axée sur la mémoire à court terme de la douleur. La complexité et la multi dimensionnalité de la douleur ajoutent encore un autre élément à la recherche sur la mémoire de la douleur. Par exemple, la trace de la mémoire de la douleur peut contenir des traces de mémoire de diverses composantes de la douleur telles que la réponse sensorielle affective, cognitive et motrice et l'interaction entre elles. Par conséquent, une première étape dans l'exploration neuroscientifique de la mémoire de la douleur nécessite la réduction de l'expérience de la douleur tout en englobant tous ces différents composants à un seul composant. Dans la recherche présentée ici, nous avons généralement examiné cela par des instructions d'attention ‘ top-down’ pour assister à la dimension sensorielle de la douleur. La recherche précédente sur la mémoire à court terme de la douleur a également porté principalement sur la dimension sensorielle de la douleur. Cependant, parmi les dimensions sensorielles de la douleur, la mémoire à court terme de l'intensité et de la dimension spatiale de la douleur a fait l'objet de recherches antérieures. Malgré son importance, la dimension temporelle de la douleur est restée complètement inexplorée dans la recherche sur la mémoire de la douleur. La recherche menée dans cette thèse est consacrée à l'exploration de la mémoire à court terme de la durée de la douleur. La durée de la douleur peut être suivie de manière indépendante, mais peut également être suivie conjointement avec la dimension d'intensité telle que le suivi dynamique de l'intensité de la douleur dans le temps. Les études menées dans cette thèse traitent spécifiquement du traitement isolé de la durée de la douleur ainsi que du traitement conjoint de la dimension durée / intensité de la douleur. La première étude psychophysique a exploré la nature de la représentation mentale du modèle de mémoire de la douleur thermique dynamique et a également été conçue pour aborder les différences de la dimension sensorielle et affective de la douleur thermique dans la mémoire à court terme. La deuxième étude psychophysique portait sur les propriétés de la mémoire à court terme de la sensation thermique non douloureux en comparant le suivi dynamique de la sensation et le suivi isolé de la durée d'un événement thermique non douloureux. La troisième étude poursuit l'exploration du traitement dynamique de la durée conjointement avec l'intensité par rapport au traitement isolé de la durée dans la mémoire à court terme en utilisant des stimuli thermiques douloureuse une résonance magnétique fonctionnelle (IRMF). Dans l'ensemble, les résultats des études psychophysiques ont montré une transformation significative de la durée et de la dynamique de la sensation thermique douloureux et non-douloureux dans la mémoire à court terme; comme la perte d'informations somatosensorielles temporelles en mémoire. Nous avons en outre montré une amélioration du rappel de la durée dans le suivi dynamique de la durée, en comparaison avec le suivi de la durée isolée. Nous avons également montré des différences dans les corrélats neuronaux de la mémoire à court terme de la durée de douleur par rapport à la dynamique de douleur. L'étude de l'IRMF a montré des similitudes frappantes dans les corrélats neuronaux sous-jacents à la mémoire à court terme de douleur et d'autres modalités telles que la contribution des coticés fronto-pariétales ainsi que les corticaux sensoriels impliqués dans le traitement perceptuel.Pain can be viewed as a protective system that signals threat and alerts us to impending tissue damage. As a defense mechanism, it necessitates the learning and memory of past painful experiences for survival and pain-related behavior. Therefore our current pain experience is heavily influenced by previous experiences and learning. However, despite its importance, our current understanding of the interaction between the pain system and the memory system is very limited. Pain memory is a very broad topic of research on its own. It requires an understanding of the mechanisms involved at each stage of the memory system (immediate, short-term, and long-term memory), and the interaction among them. Among the multiple stages of memory, the short-term memory of pain is an area that is less researched, while there are enormous amount of neuroscientific research in short-term memory of other modalities, particularly vision. Investigation of the short-term memory of pain is especially important as the short-term memory trace of pain is converted to long-term memory and subsequently affects future pain experiences. This thesis is broadly focused on the short-term memory of pain. The complexity and multi-dimensionality of pain adds yet another element to the research on pain memory. For example, the memory trace of pain may contain memory traces of various components of pain such as sensory, affective, cognitive, and motoric responses, and the interactions among them. Therefore, an initial step in the neuroscientific exploration of pain memory requires narrowing down the pain experience, which encompasses all of these various components, to one single component. In the research presented here, we achieved this using top-down attentional instructions to attend to the sensory component of pain. The previous research on short-term memory of pain also focused mainly on the sensory component of pain. However, within the sensory component of pain the short-term memory of intensity and spatial dimension of pain has been the focus of previous research. Despite its importance, the temporal dimension of pain remained completely unexplored in pain memory research. Thus, the research conducted in this thesis is devoted to the exploration of short-term memory of the duration of pain. Pain duration can be tracked independently, but it can also be tracked conjointly with intensity, such as in dynamic tracking of pain intensity over time. The studies addressed in this thesis examined the isolated processing of pain duration as well as conjoint processing of the duration and intensity of pain. The first psychophysical study explored the nature of the mental representation of the memory template of dynamic thermal pain sensation and, additionally, addressed the differences between the sensory versus affective dimensions of thermal pain sensation in short-term memory. The second psychophysical study focused on properties of the short-term memory of innocuous thermal sensation by comparing dynamic tracking of sensation versus isolated tracking of duration of an innocuous thermal event. The third study explored the dynamic processing of duration conjointly with intensity, versus the isolated processing of duration in short-term memory, using noxious thermal stimuli and functional magnetic resonance imaging (fMRI). Overall, the results of the psychophysical studies showed significant transformation of duration and dynamics information of noxious and innocuous thermal sensation in short-term memory, such as loss of temporal somatosensory information. Additionally, we showed improvement in duration recall during dynamic tracking versus isolated tracking of duration. The fMRI study revealed differences in neural correlates of short-term memory of pain duration versus pain dynamics. Importantly, it also showed striking similarities between neural correlates underlying the short-term memory of pain and those underlying other modalities, such as a contribution of fronto-parietal cortices as well as sensory cortices involved in perceptual processing