Effects of unilateral tDCS over left prefrontal cortex on emotion regulation in depression: Evidence from concurrent functional magnetic resonance imaging.

Major depressive disorder (MDD) is the most common mood disorder and a primary cause of disability worldwide. MDD symptomatology entails disturbances in emotion regulation, namely one's ability to modify the intensity and duration of emotional reactions towards affective events. Transcranial direct current stimulation (tDCS) has emerged as a promising treatment for MDD. Yet, positive tDCS outcomes vary across studies, while the precise effects of the procedure for cortical excitability in MDD during emotion regulation remain largely unexplored. Here, we leveraged functional magnetic resonance imaging (fMRI)-compatible tDCS technology to examine the functional consequences of a unilateral anodal tDCS montage at 1.5 mA over left PFC (area F3; with the reference electrode over an extracephalic location) for brain activity during an emotion-regulation task in MDD patients and age-matched healthy control subjects. Our results revealed down-regulation of negative emotions in the right amygdala and visual cortex of healthy controls but not MDD patients prior to stimulation, the degree of which correlated with the magnitude of the participants' reappraisal scores. TDCS did not elicit significant changes in neural activation patterns for either group. These findings contribute to the literature on the pathophysiology of MDD by showing that a key disturbance in the disorder entails the ineffective down-regulation of activity not only within the amygdala, but also within visual cortical areas in response to negative information. Further, these results suggest that relative to bifrontal tDCS montages, unilateral stimulation of moderate intensity over left PFC may not be sufficient to elicit therapeutic effects for MDD.

Impaired Comprehension of Speed Verbs in Parkinson's Disease.

OBJECTIVES: A wealth of studies provide evidence for action simulation during language comprehension. Recent research suggests such action simulations might be sensitive to fine-grained information, such as speed. Here, we present a crucial test for action simulation of speed in language by assessing speed comprehension in patients with Parkinson's disease (PD). Based on the patients' motor deficits, we hypothesized that the speed of motion described in language would modulate their performance in semantic tasks. Specifically, they would have more difficulty processing language about relatively fast speed than language about slow speed. METHODS: We conducted a semantic similarity judgment task on fast and slow action verbs in patients with PD and age-matched healthy controls. Participants had to decide which of two verbs most closely matched a target word. RESULTS: Compared to controls, PD patients were slower making judgments about fast action verbs, but not for judgments about slow action verbs, suggesting impairment in processing language about fast action. Moreover, this impairment was specific to verbs describing fast action performed with the hand. CONCLUSIONS: Problems moving quickly lead to difficulties comprehending language about moving quickly. This study provides evidence that speed is an important part of action representations. (JINS, 2017, 23, 412-420).

The Semantics of Syntax: The Grounding of Transitive and Intransitive Constructions.

Embodied theories of language maintain that brain areas associated with perception and action are also involved in the processing and representation of word meaning. A number of studies have shown that sentences with action verbs elicit activation within sensory-motor brain regions, arguing that sentence-induced mental simulations provide a means for grounding their lexical-semantic meaning. Constructionist theories argue, however, that form-meaning correspondence is present not only at the lexical level but also at the level of constructions. We investigated whether sentence-induced motor resonance is present for syntactic constructions. We measured the BOLD signal while participants read sentences with (di)transitive (caused motion) or intransitive constructions that contained either action or abstract verbs. The results showed a distinct neuronal signature for caused motion and intransitive syntactic frames. Caused motion frames activated regions associated with reaching and grasping actions, including the left anterior intraparietal sulcus and the parietal reach region. Intransitive frames activated lateral temporal regions commonly associated with abstract word processing. The left pars orbitalis showed an interaction between the syntactic frame and verb class. These findings show that sensory-motor activation elicited by sentences entails both motor resonance evoked by single words as well as at the level of syntactic constructions.

Resting state signatures of domain and demand-specific working memory performance.

Working memory (WM) is one of the key constructs in understanding higher-level cognition. We examined whether patterns of activity in the resting state of individual subjects are correlated with their off-line working and short-term memory capabilities. Participants completed a resting-state fMRI scan and off-line working and short-term memory (STM) tests with both verbal and visual materials. We calculated fractional amplitude of low frequency fluctuations (fALFF) from the resting state data, and also computed connectivity between seeds placed in frontal and parietal lobes. Correlating fALFF values with behavioral measures showed that the fALFF values in a widespread fronto-parietal network during rest were positively correlated with a combined memory measure. In addition, STM showed a significant correlation with fALFF within the right angular gyrus and left middle occipital gyrus, whereas WM was correlated with fALFF values within the right IPS and left dorsomedial cerebellar cortex. Furthermore, verbal and visuospatial memory capacities were associated with dissociable patterns of low-frequency fluctuations. Seed-based connectivity showed correlations with the verbal WM measure in the left hemisphere, and with the visual WM measure in the right hemisphere. These findings contribute to our understanding of how differences in spontaneous low-frequency fluctuations at rest are correlated with differences in cognitive performance.

Context-dependent changes in functional connectivity of auditory cortices during the perception of object words.

Embodied theories hold that cognitive concepts are grounded in our sensorimotor systems. Specifically, a number of behavioral and neuroimaging studies have buttressed the idea that language concepts are represented in areas involved in perception and action [Pulvermueller, F. Brain mechanisms linking language and action. Nature Reviews Neuroscience, 6, 576-582, 2005; Barsalou, L. W. Perceptual symbol systems. Behavioral and Brain Sciences, 22, 577-660, 1999]. Proponents of a strong embodied account argue that activity in perception/action areas is triggered automatically upon encountering a word and reflect static semantic representations. In contrast to what would be expected if lexical semantic representations are automatically triggered upon encountering a word, a number of studies failed to find motor-related activity for words with a putative action-semantic component [Raposo, A., Moss, H. E., Stamatakis, E. A., & Tyler, L. K. Modulation of motor and premotor cortices by actions, action words and action sentences. Neuropsychologia, 47, 388-396, 2009; Rueschemeyer, S.-A., Brass, M., & Friederici, A. D. Comprehending prehending: Neural correlates of processing verbs with motor stems. Journal of Cognitive Neuroscience, 19, 855-865, 2007]. In a recent fMRI study, Van Dam and colleagues [Van Dam, W. O., Van Dijk, M., Bekkering, H., & Rueschemeyer, S.-A. Flexibility in embodied lexical-semantic representations. Human Brain Mapping, in press] showed that the degree to which a modality-specific region contributes to a representation considerably changes as a function of context. In the current study, we presented words for which both motor and visual properties (e.g., tennis ball, boxing glove) were important in constituting the concept. Our aim was to corroborate on earlier findings of flexible and context-dependent language representations by testing whether functional integration between auditory brain regions and perception/action areas is modulated by context. Functional connectivity was investigated by means of a psychophysiological interaction analysis, in which we found that bilateral superior temporal gyrus was more strongly connected with brain regions relevant for coding action information: (1) for Action Color words vs. Abstract words, and (2) for Action Color words presented in a context that emphasized action vs. a context that emphasized color properties.

Flexibility in embodied lexical-semantic representations.

According to an embodied view of language comprehension, language concepts are grounded in our perceptual systems. Evidence for the idea that concepts are grounded in areas involved in action and perception comes from both behavioral and neuroimaging studies (Glenberg [1997]: Behav Brain Sci 20:1-55; Barsalou [1999]: Behav Brain Sci 22:577-660; Pulvermueller [1999]: Behav Brain Sci 22:253-336; Barsalou et al. [2003]: Trends Cogn Sci 7:84-91). However, the results from several studies indicate that the activation of information in perception and action areas is not a purely automatic process (Raposo et al. [2009]: Neuropsychologia 47:388-396; Rueschemeyer et al. [2007]: J Cogn Neurosci 19:855-865). These findings suggest that embodied representations are flexible. In these studies, flexibility is characterized by the relative presence or absence of activation in our perceptual systems. However, even if the context in which a word is presented does not undermine a motor interpretation, it is possible that the degree to which a modality-specific region contributes to a representation depends on the context in which conceptual features are retrieved. In the present study, we investigated this issue by presenting word stimuli for which both motor and visual properties (e.g., Tennis ball, Boxing glove) were important in constituting the concept. Conform with the idea that language representations are flexible and context dependent, we demonstrate that the degree to which a modality-specific region contributes to a representation considerably changes as a function of context.

Transcranial Direct Current Stimulation Over the Prefrontal Cortex in Depression Modulates Cortical Excitability in Emotion Regulation Regions as Measured by Concurrent Functional Magnetic Resonance Imaging: An Exploratory Study.

BACKGROUND: A well-established impaired top-down network for effortful emotion regulation (ER) in major depressive disorder (MDD) includes the dorsal and ventromedial prefrontal cortex (PFC) and the amygdala. Transcranial direct current stimulation (tDCS) is a noninvasive neuromodulation method that has been used successfully to induce mood changes in MDD. Despite reliable findings, little is known regarding the precise effects of tDCS on cortical excitability in vivo in depression and how such changes relate to ER. Here, we addressed this question by combining-for the first time in a psychiatric sample-tDCS with functional magnetic resonance imaging in a single-blind randomized design. METHODS: We applied anodal tDCS over the left PFC (area F3 per the 10/20 system) together with cathodal tDCS over the right PFC (F4) or sham tDCS during functional magnetic resonance imaging in patients with moderate to severe MDD (n = 20) and gender- and age-matched control subjects (n = 20). Participants performed 2 runs of an ER task prior to tDCS and 2 runs of the task during tDCS, which was administered at 1.5 mA with 5-cm × 5-cm electrodes. RESULTS: Whole-brain, region of interest, and connectivity analyses revealed an impaired ER network in patients with MDD prior to stimulation. Active anodal tDCS over the left (with concurrent cathodal stimulation of the right) PFC during reappraisal of negative stimuli upregulated activity in ventromedial PFC, which was predictive of gains in reappraisal performance during stimulation for the patients with MDD. CONCLUSIONS: The results of this study offer insights into the mechanisms of action of tDCS and support its potential as a treatment for depression.

How specifically are action verbs represented in the neural motor system: an fMRI study.

Embodied accounts of language processing suggest that sensorimotor areas, generally dedicated to perception and action, are also involved in the processing and representation of word meaning. Support for such accounts comes from studies showing that language about actions selectively modulates the execution of congruent and incongruent motor responses (e.g., Glenberg & Kaschak, 2002), and from functional neuroimaging studies showing that understanding action-related language recruits sensorimotor brain areas (e.g. Hauk, Johnsrude, & Pulvermueller, 2004). In the current experiment we explored the basis of the neural motor system's involvement in representing words denoting actions. Specifically, we investigated whether the motor system's involvement is modulated by the specificity of the kinematics associated with a word. Previous research in the visual domain indicates that words denoting basic level category members lacking a specific form (e.g., bird) are less richly encoded within visual areas than words denoting subordinate level members (e.g., pelican), for which the visual form is better specified (Gauthier, Anderson, Tarr, Skudlarski, & Gore, 1997). In the present study we extend these findings to the motor domain. Modulation of the BOLD response elicited by verbs denoting a general motor program (e.g., to clean) was compared to modulation elicited by verbs denoting a more specific motor program (e.g., to wipe). Conform with our hypothesis, a region within the bilateral inferior parietal lobule, typically serving the representation of action plans and goals, was sensitive to the specificity of motor programs associated with the action verbs. These findings contribute to the growing body of research on embodied language representations by showing that the concreteness of an action-semantic feature is reflected in the neural response to action verbs.

Distinct neural mechanisms underlying conceptual knowledge of manner and instrument verbs.

Studies on the organization of conceptual knowledge have examined categories of concrete nouns extensively. Less is known about the neural basis of verb categories suggested by linguistic theories. We used functional MRI to examine the differences between manner verbs, which encode information about the manner of an action, versus instrument verbs, which encode information about an object as part of their meaning. Using both visual and verbal stimuli and a combination of univariate and multivariate pattern analyses, our results show that accessing conceptual representations of instrument class involves brain regions typically associated with complex action and object perception, including the anterior inferior parietal cortex and occipito-temporal cortex. On the other hand, accessing conceptual representations of the manner class involves regions that are commonly associated with the processing of visual and biological motion, in the posterior superior temporal sulcus. These findings support the idea that the semantics of manner and instrument verbs are supported by distinct neural mechanisms.

Embodied Simulations Are Modulated by Sentential Perspective.

There is considerable evidence that language comprehenders derive lexical-semantic meaning by mentally simulating perceptual and motor attributes of described events. However, the nature of these simulations-including the level of detail that is incorporated and contexts under which simulations occur-is not well understood. Here, we examine the effects of first- versus third-person perspective on mental simulations during sentence comprehension. First-person sentences describing physical transfer towards or away from the body (e.g., "You threw the microphone," "You caught the microphone") modulated response latencies when responses were made along a front-back axis, consistent with the action-sentence compatibility effect (ACE). This effect was not observed for third-person sentences ("He threw the microphone," "He caught the microphone"). The ACE was observed when making responses along a left-right axis for third-person, but not first-person sentences. Abstract sentences (e.g., "He heard the message") did not show an ACE along either axis. These results show that perspective is a detail that is simulated during action sentence comprehension, and that motoric activations are flexible and affected by the pronominal perspective used in the sentence.

Effects of motion speed in action representations.

Grounded cognition accounts of semantic representation posit that brain regions traditionally linked to perception and action play a role in grounding the semantic content of words and sentences. Sensory-motor systems are thought to support partially abstract simulations through which conceptual content is grounded. However, which details of sensory-motor experience are included in, or excluded from these simulations, is not well understood. We investigated whether sensory-motor brain regions are differentially involved depending on the speed of actions described in a sentence. We addressed this issue by examining the neural signature of relatively fast (The old lady scurried across the road) and slow (The old lady strolled across the road) action sentences. The results showed that sentences that implied fast motion modulated activity within the right posterior superior temporal sulcus and the angular and middle occipital gyri, areas associated with biological motion and action perception. Sentences that implied slow motion resulted in greater signal within the right primary motor cortex and anterior inferior parietal lobule, areas associated with action execution and planning. These results suggest that the speed of described motion influences representational content and modulates the nature of conceptual grounding. Fast motion events are represented more visually whereas motor regions play a greater role in representing conceptual content associated with slow motion.

Flexibility in embodied language processing: context effects in lexical access.

According to embodied theories of language (ETLs), word meaning relies on sensorimotor brain areas, generally dedicated to acting and perceiving in the real world. More specifically, words denoting actions are postulated to make use of neural motor areas, while words denoting visual properties draw on the resources of visual brain areas. Therefore, there is a direct correspondence between word meaning and the experience a listener has had with a word's referent on the brain level. Behavioral and neuroimaging studies have provided evidence in favor of ETLs; however, recent studies have also shown that sensorimotor information is recruited in a flexible manner during language comprehension (e.g., Raposo et al.; Van Dam et al.,), leaving open the question as to what level of language processing sensorimotor activations contribute. In this study, we investigated the time course of modality-specific contributions (i.e., the contribution of action information) as to word processing by manipulating both (a) the linguistic and (b) the action context in which target words were presented. Our results demonstrate that processes reflecting sensorimotor information play a role early in word processing (i.e., within 200 ms of word presentation), but that they are sensitive to the linguistic context in which a word is presented. In other words, when sensorimotor information is activated, it is activated quickly; however, specific words do not reliably activate a consistent sensorimotor pattern.

Embodied grounding of memory: toward the effects of motor execution on memory consolidation.

Behavioural and neuroscientific research has provided evidence for a strong functional link between the neural motor system and lexical-semantic processing of action-related language. It remains unclear, however, whether the impact of motor actions is restricted to online language comprehension or whether sensorimotor codes are also important in the formation and consolidation of persisting memory representations of the word's referents. The current study now demonstrates that recognition performance for action words is modulated by motor actions performed during the retention interval. Specifically, participants were required to learn words denoting objects that were associated with either a pressing or a twisting action (e.g., piano, screwdriver) and words that were not associated to actions. During a 6-8-minute retention phase, participants performed an intervening task that required the execution of pressing or twisting responses. A subsequent recognition task revealed a better memory for words that denoted objects for which the functional use was congruent with the action performed during the retention interval (e.g., pepper mill-twisting action, doorbell-pressing action) than for words that denoted objects for which the functional use was incongruent. In further experiments, we were able to generalize this effect of selective memory enhancement of words by performing congruent motor actions to an implicit perceptual (Experiment 2) and implicit semantic memory test (Experiment 3). Our findings suggest that a reactivation of motor codes affects the process of memory consolidation and emphasizes therefore the important role of sensorimotor codes in establishing enduring semantic representations.

Mental rotation impairs attention shifting and short-term memory encoding: neurophysiological evidence against the response-selection bottleneck model of dual-task performance.

Dual tasks and their associated delays have often been used to examine the boundaries of processing in the brain. We used the dual-task procedure and recorded event-related potentials (ERPs) to investigate how mental rotation of a first stimulus (S1) influences the shifting of visual-spatial attention to a second stimulus (S2). Visual-spatial attention was monitored by using the N2pc component of the ERP. In addition, we examined the sustained posterior contralateral negativity (SPCN) believed to index the retention of information in visual short-term memory. We found modulations of both the N2pc and the SPCN, suggesting that engaging mechanisms of mental rotation impairs the deployment of visual-spatial attention and delays the passage of a representation of S2 into visual short-term memory. Both results suggest interactions between mental rotation and visual-spatial attention in capacity-limited processing mechanisms indicating that response selection is not pivotal in dual-task delays and all three processes are likely to share a common resource like executive control.

How object-specific are object files? Evidence for integration by location.

Given the distributed representation of visual features in the human brain, binding mechanisms are necessary to integrate visual information about the same perceptual event. It has been assumed that feature codes are bound into object files--pointers to the neural codes of the features of a given event. The present study investigated the perceptual criteria underlying integration into an object file. Previous studies confounded the sharing of spatial location with belongingness to the same perceptual object, 2 factors we tried to disentangle. Our findings suggest that orientation and color features appearing in a task-irrelevant preview display were integrated irrespective of whether they appeared as part of the same object or of different objects (e.g., 1 stationary and the other moving continuously, or a banana in a particular orientation overlaying an apple of a particular color). In contrast, integration was markedly reduced when the 2 objects were separated in space. Taken together, these findings suggest that spatial overlap of visual features is a sufficient criterion for integrating them into the same object file.

Context effects in embodied lexical-semantic processing.

The embodied view of language comprehension proposes that the meaning of words is grounded in perception and action rather than represented in abstract amodal symbols. Support for embodied theories of language processing comes from behavioral studies showing that understanding a sentence about an action can modulate congruent and incongruent physical responses, suggesting motor involvement during comprehension of sentences referring to bodily movement. Additionally, several neuroimaging studies have provided evidence that comprehending single words denoting manipulable objects elicits specific responses in the neural motor system. An interesting question that remains is whether action semantic knowledge is directly activated as motor simulations in the brain, or rather modulated by the semantic context in which action words are encountered. In the current paper we investigated the nature of conceptual representations using a go/no-go lexical decision task. Specifically, target words were either presented in a semantic context that emphasized dominant action features (features related to the functional use of an object) or non-dominant action features. The response latencies in a lexical decision task reveal that participants were faster to respond to words denoting objects for which the functional use was congruent with the prepared movement. This facilitation effect, however, was only apparent when the semantic context emphasized corresponding motor properties. These findings suggest that conceptual processing is a context-dependent process that incorporates motor-related knowledge in a flexible manner.