Semantic retrieval involves both (1) automatic spreading activation between highly related concepts and (2) executive control processes that tailor this activation to suit the current context or goals. Two structures in left temporoparietal cortex, angular gyrus (AG) and posterior middletemporalgyrus (pMTG), are thought to be crucial to semantic retrieval and are often recruited together during semantic tasks; however, they show strikingly different patterns of functional connectivity at rest (coupling with the “default mode network” and “frontoparietal control system,” respectively). Here, transcranial magnetic stimulation (TMS) was used to establish a causal yet disso- ciable role for these sites in semantic cognition in human volunteers. TMS to AG disrupted thematic judgments particularly when the link between probe and target was strong (e.g., a picture of an Alsatian with a bone), and impaired the identification of objects at a specific but not a superordinate level (for the verbal label “Alsatian” not “animal”). In contrast, TMS to pMTG disrupted thematic judgments for weak but not strong associations (e.g., a picture of an Alsatian with razor wire), and impaired identity matching for both superordinate and specific-level labels. Thus, stimulation to AG interfered with the automatic retrieval of specific concepts from the semantic store while stimulation of pMTG impaired semantic cognition when there was a requirement to flexibly shape conceptual activation in line with the task requirements. These results demonstrate that AG and pMTG make a dissociable contribution to automatic and controlled aspects of semantic retrieval.
Compared to the healthy controls, our study showed that late- stage patients significantly decreased connections between left PMTG and right middletemporalgyrus networks, which was not discovered in the early stage of aphasia after stroke. The decrease is likely due to the loss of FC between the nodes. In addition, this might reflect the progression of aphasia after stroke and decreased functional activity occurs gradually not only in the regions with brain lesions but also in the associated regions in the right hemisphere. This might be the consequence of neuroplasticity, which the brain activity can be transferred to a different location. 32
This study set out to better characterise the functional role of the posterior middletemporalgyrus (pMTG) in semantic processing. Left pMTG is thought to play a key role in both controlled aspects of semantic retrieval and the comprehension of events, relations and actions – but the specific relationship between structure and function remains an open question. Although the field of semantic cognition is converging on a component process account, involving conceptual representations plus control mechanisms which can shape the pattern of retrieval to suit the task or context, the brain mechanisms that underpin this capacity remain poorly understood. Our analysis suggests that pMTG is a functional nexus drawing together two well-documented large-scale networks implicated in automatic semantic processing and executive control, and thus allowing more controlled patterns of retrieval. In task-based fMRI, we identified pMTG through the conjunction of judgements about global semantic associations and action features and found that under these conditions it showed greater functional coupling with inferior regions of the left frontal prefrontal cortex that included aspects of both the DMN and the MDN. This region overlapped with an area implicated in semantic control by a recent meta-analysis (Noonan et al., 2013). Resting state functional connectivity in an independent data set revealed that the same region was intrinsically coupled at rest to seed regions exhibiting peak activity in hard > easy semantic judgements (in inferior frontal sulcus, IFS, within the multiple-demand executive network) and easy > hard decisions (in anterior temporal lobe; ATL). A similar analysis using diffusion MRI data demonstrated that long-range connections from IFS and ATL overlapped in white matter adjacent to pMTG. Together these findings show that in topological terms, pMTG is located at the intersection of the DMN and MDN, a position that would allow it to integrate information from otherwise anti-correlated large-scale systems.
Finally, there is a growing literature on the effects of non-invasive brain stimulation on lexical-semantic retrieval and selection, which is broadly consistent with the dissociation between left prefrontal and temporoparietal cortex found in neuropsychological investigations. Anodal transcranial direct current stimulation (tDCS) to left prefrontal cortex has been shown to decrease effects of semantic interference in semantically-blocked picture naming, including dampening down increases in naming latencies that characterise the effects of repeating semantically-related sets of pictures (Pisoni et al., 2012; Wirth et al., 2011, although null results for LIFG were reported by Henseler et al., 2014). These effects might reflect a strengthening of top-down control following LIFG stimulation, since anodal tDCS is thought to enhance cortical excitability and thus facilitate processes within stimulated brain sites. In contrast, tDCS to the posterior superior temporal lobe was found to increase semantic interference effects (Pisoni et al., 2012), perhaps because greater excitability of this region led to more spreading activation between semantically-related items, and thus more competition. However, interpretation of these findings is not straightforward as tDCS is not a focal method, and not well-suited to drawing conclusions about the functions of specific brain regions. Neuroimaging studies have revealed multiple regions in both posterior temporal and prefrontal cortex with different roles (Badre et al., 2005; Bedny et al., 2008; Gold et al., 2006): for example, Bedny et al. (2008) found that while left posterior STG showed effects of semantic similarity, pMTG showed effects of ambiguity like LIFG. However, tDCS to the posterior temporal lobe would
In Chapter 3.5, I discussed the possible reasons why the fMRI-guided TMS study led to non-significant results. I strongly believe that TMS is a suitable tool to directly compare the role of different brain areas and the behavioral consequences of the stimulation of different sites during the same task. In particular, observing the effect of the stimulation of the temporal and precentral areas on semantic tasks might be the key to shed light on the debate between motor and cognitive theories. For this reason, I think that the approach we developed in the study presented in Chapter 3, Experiment 2 was strong and consistent with the scientific question we were trying to assess. As a future direction, I would work on developing an improved paradigm in order to facilitate the investigation on the effect of the perturbation of the pMTG and PMC during action recognition. One possibility would be to modify the stimuli used in order to make the task more difficult thereby increasing the possibility of observing an effect of the stimulation. Another possibility would be to opt for a different stimulation protocol, such as single pulse online protocol or theta burst stimulation, which might lead to larger effects.
The next question we examined was whether boys and girls showed differences in developmental patterns across the cortical mantle. Model 3 (including the age by sex interaction effect) was never the best fitting model with the exception of one structure: the surface area of the left banks superior temporalgyrus. This region showed a steeper decline in boys than girls (see Figure 1 and Table 3A). For the following regions, we observed significant age by sex interaction effects showing steeper declines for boys than girls, but this was not the best fitting model: surface area of the bilateral caudal middle frontal gyrus, left pericalcarine gyrus, left precuneus, right banks superior temporalgyrus, right isthmus cingulate gyrus, right lateral occipital cortex, right pars opercularis, right pericalcarine region (see Table 3A). Thickness showed significant age by sex interaction effects (but not best model fits) for the bilateral posterior cingulate gyrus, bilateral rostral anterior cingulate gyrus, left medial orbitofrontal gyrus, right inferior parietal gyrus, right middletemporalgyrus, and right frontal pole (see Table 3B).
Whereas the moderate practice given in the present study indeed reduced prefrontal activations, it did not produce clear-cut shifts of activations to other cortical regions, in the sense of a genuine reorganisation (Kelly and Garavan, 2005). Although stronger activations for practised vs. non-practised chords were observed in a number of cortical areas, none of these differential activations corresponded to positive activations in the basic contrasts. Therefore, these findings must be treated with caution. A minimalist explanation would be that both elementary finger postures and learned configurations of these postures (i.e., complete chords) are represented in the MNS. Hence, large-scale shifts of activations to areas other than the MNS would not be expected as a result of practice. A likely exception might be an additional coding of highly practised actions in superior temporal regions (e.g., Calvo-Merino et al., 2005), which presumably requires longer practice periods than employed in the present study. Nevertheless, the stronger activation for practised chords in the left angular gyrus and the right posterior middletemporalgyrus in our study might be an early indication of such an experience-dependent plasticity of higher order visual areas.
Notes: Significant differences in activity were observed in the right inferior and middletemporalgyrus, left middletemporalgyrus, left inferior frontal gyrus/putamen, right inferior frontal gyrus/putamen/insula, right middle frontal gyrus, right inferior parietal lobule, bilateral midcingulate cortex, left postcentral gyrus, and left precuneus/inferior parietal lobule. The red or yellow areas denote higher alFF values and the blue areas indicate lower alFF values (P 0.01 for multiple comparisons using grF theory) (z 2.3, P0.01, cluster 40 voxels, alphasim corrected).
Results: Compared with the healthy controls, patients with ON showed lower ReHo in the left cerebellum, posterior lobe, left middletemporalgyrus, right insula, right superior temporalgyrus, left middle frontal gyrus, bilateral anterior cingulate cortex, left superior frontal gyrus, right superior frontal gyrus, and right precentral gyrus, and higher ReHo in the cluster of the left fusiform gyrus and right inferior parietal lobule. Meanwhile, we found that the VEP amplitude of the right eye in patients with ON showed a positive correlation with the ReHo signal value of the left cerebellum posterior lobe (r=0.701, P=0.011), the right superior frontal gyrus (r=0.731, P=0.007), and the left fusiform gyrus (r=0.644, P=0.024). We also found that the VEP latency of the right eye in ON showed a positive correlation with the ReHo signal value of the right insula (r=0.595, P=0.041). Conclusion: ON may involve dysfunction in the default-mode network, which may reflect the underlying pathologic mechanism.
Neuroimaging studies have indicated abnormalities in cortico-striato-thalamo-cortical circuits in obsessive– compulsive disorder patients, but results have not been consistent. Since there are significant sex differ- ences in human brain anatomy and obsessive–compulsive symptomatology and its developmental tra- jectories tend to be distinct in males and females, we investigated whether sex is a potential source of heterogeneity in neuroimaging studies on obsessive–compulsive symptoms. We selected male and fe- male twin pairs who were concordant for scoring either high or low for obsessive–compulsive symptoms and a group of discordant pairs where one twin scored high and the co-twin scored low. The design included 24 opposite-sex twin pairs. Magnetic resonance imaging scans of 31 males scoring high for obsessive–compulsive symptoms, 41 low-scoring males, 58 high-scoring females, and 73 low-scoring fe- males were analyzed and the interaction of obsessive–compulsive symptoms by sex on gray matter volume was assessed using voxel-based morphometry. An obsessive–compulsive symptom by sex interaction was observed for the left middletemporalgyrus, the right middletemporalgyrus, and the right precuneus. These interactions acted to reduce or hide a main effect in our study and illustrate the importance of taking sex into account when investigating the neurobiology of obsessive–compulsive symptoms.
A direct comparison between the after treatment and baseline images in the AD group, although not surviving correction for multiple comparisons, identiﬁ ed a number of regions which had signiﬁ cantly increased in activation after treatment. The locations of these areas were consistent with sites which published fMRI studies have reported as signiﬁ cantly activated by healthy controls when performing a semantic association paradigm similar to that used in the present study. Increased activation was found in the left inferior frontal gyrus, the left middletemporalgyrus, the right superior frontal gyrus and in the middle frontal, the fusiform and the parahippocampal gyri bilaterally (Table 2b, Figure 2a). The baseline versus retest comparison showed no differences surviving a corrected threshold of signiﬁ cance. Differences were present in the right postcentral gyrus and the right inferior parietal lobule at an uncorrected thresh- old level. To check whether these differences were due to greater deactivation in the AD group after treatment, the deactivation pattern from the random effects analysis was used as a mask (ie, signiﬁ cant areas of deactivation were used as a mask in the analyses to ensure that any signiﬁ cant differences referred only to actual increases in activation). After masking for deactivation, these differences were no longer detectable.
GG (figure 3 and table e-3). The inverse comparisons did not yield results at the pre-established threshold. Structural correlation analysis to assess interhemi- spheric and intrahemispheric connectivity according to KIAA0319 genotype was carried out. In patients with PPA carrying at-risk KIAA0319 A* genotype, decreased structural GM correlation between the left middletemporalgyrus (peak MNI coordinates x, y, z: 256, 2, 220) and other both interhemispheric and intrahemispheric brain regions was highlighted, as compared with patients with PPA carrying KIAA0319 GG. The same pattern was seen for WM density (figure 4 and table e-4).
Introduction: Drug craving could be described as a motivational state which drives drug dependents towards drug seeking and use. Different types of self-reports such as craving feeling, desire and intention, wanting and need, imagery of use, and negative affect have been attributed to this motivational state. By using subjective self-reports for different correlates of drug craving along with functional neuroimaging with cue exposure paradigm, we investigated the brain regions that could correspond to different dimensions of subjective reports for heroin craving. Methods: A total of 25 crystalline-heroin smokers underwent functional magnetic resonance imaging (fMRI), while viewing heroin-related and neutral cues presented in a block-design task. During trial intervals, subjects verbally reported their subjective feeling of cue induced craving (CIC). After fMRI procedure, participants reported the intensity of their “need for drug use” and “drug use imagination” on a 0-100 visual analog scale (VAS). Afterwards, they completed positive and negative affect scale (PANAS) and desire for drug questionnaire (DDQ) with 3 components of “desire and intention to drug use,” “negative reinforcement,” and “loss of control.” Results: The study showed significant correlation between “subjective feeling of craving” and activation of the left and right anterior cingulate cortex, as well as right medial frontal gyrus. Furthermore, the “desire and intention to drug use” was correlated with activation of the left precentral gyrus, left superior frontal gyrus, and left middle frontal gyrus. Subjects also exhibited significant correlation between the “need for drug use” and activation of the right inferior temporalgyrus, right middletemporalgyrus, and right parahippocampal gyrus. Correlation between subjective report of “heroin use imagination” and activation of the cerebellar vermis was also observed. Another significant correlation was between the “negative affect” and activation of the left precuneus, right putamen, and right middletemporalgyrus.
A 3D volume-rendered image of each cerebral hemisphere was displayed on a high-resolution color monitor. One neuro- radiologist (K.I.) blinded to the clinical data and diagnosis rated regional cortical atrophy for each of the 66 cortical regions of the lateral and medial hemispheric surfaces into five categories: normal (nadir of the sulcus invisible with stacked gyri), minimal (nadir of the sulcus visible), mild (bottom of the sulcus widened), moderate (gyrus thinner than sulcus), and severe (very shrunken). The regions consisted of the orbito- frontal cortex, superior frontal gyrus (anterior and posterior, lateral and medial), middle frontal gyrus (anterior and poste- rior), inferior frontal gyrus (anterior and posterior), cingulate gyrus (anterior and posterior), precentral gyrus (medial and lateral), postcentral gyrus (medial and lateral), superior pari- etal lobule (anterior and posterior, lateral and medial), inferior parietal lobule (anterior and posterior), superior temporal gy- rus (anterior and posterior), middletemporalgyrus (anterior and posterior), inferior temporalgyrus (anterior and poste- rior), parahippocampal gyrus (anterior and posterior), occipital gyri (anterior and posterior, lateral and medial), midbrain, and pons on either side. The score of the more affected side was considered representative for a given region, so that altogether 33 regions were evaluated.
Our results help to clarif y neural activations previously associated with theory of mind and agency detection. The results suggest that perception of inanimate, mechanical contingency is largely automatic, unaffected by subjects’ expectations and attention, and engages regions of the middletemporalgyrus and intraparietal sulcus. The detection of animate contingency also includes automatic, bottom-up neural processing, which is unaffected by attention to contingency, largely confined to parietal networks dedicated to complex visuo-spatial detection. In contrast, activations in the right middle frontal gyrus and left STS appear to be a result of attending to possible agents in animate–contingent displays as opposed to detecting them on the basis of visual cues. An impairment of theory of mind has been proposed to be a central underlying cause of the social interaction difficulties experienced in autism (Baron-Cohen et al., 1985; Frith, 2001). The current results may be of interest in the understanding both of normal theory of mind functions and of their impairment.
Abstract: Objective: The present study aimed to determine whether Default-Mode Network (DMN) connectivity at resting-state is altered in college students with mobile phone addiction (MPA) by functional magnetic resonance imaging (fMRI). Methods: The fMRI data were acquired during resting state from 24 college students with MPA and 16 age- and gender-matched normal control college students. Synchronized low-frequency fMRI signal fluctuations were monitored to determine posterior cingulate cortex (PCC) connectivity in all subjects. In order to assess the relationship between MPA behavioral features and alteration in functional connectivity, the z value of areas that ex- hibited abnormal PCC connectivity in 24 subjects with MPA were correlated with the scores of the Self-Rating Anxiety Scale (SAS), Self-rating Depression Scale (SDS), Barratt Impulsiveness Scale-11 (BIS-11), Rosenberg Self-esteem Scale, Pittsburgh sleep quality index (PSQI), Sensation Seeking (SS), Smartphone Addiction Inventory (SPAI) and Mobile Phone Addiction Index (MPAI). Results: Compared with the control group, functional connectivity in the an- terior cingulate, bilateral middle frontal gyrus, bilateral inferior frontal gyrus, right middletemporalgyrus, and right inferior temporalgyrus increased in subjects with MPA. Subjects with MPA revealed higher SAS (P = 0.0293), SDS (P = 0.0056), BIS-11 (P<0.0001), PSQI (P = 0.001), SPAI (P<0.0001) and MPAI (P<0.0001) scores and lower RSS (P = 0.0002) scores, compared to controls. No significant correlations were found between altered functional con- nectivity and MPA behavioral features. Conclusion: College students with MPA present different behavioral features and DMN functional connectivity, especially in cerebral regions related to cognitive control.
At a more empirical level, drawings may be based on direct visual inputs such as edges, line segments, line drawings, portraits, photographs, or three-dimensional objects that are presented immediately, or that are subsequently removed after short durations.. These types of drawing from copy, after a delay, characterize most of the neuropsychological tasks associated with CA and used presently. With such brief temporal durations, participants would be expected to rely to a greater extent on visuospatial encoding and memory processes. Alternatively, for the production of facsimiles of real objects, participants may rely on memory retrieval using language and speech based mechanisms that evoke longer term visual representations . Casagrande (2010) hypothesized that such visual representations may be conjured up from the subconscious during hypnogogic imagery or during rapid eye movement related dreaming and sleep as is described in the account of how James Watson visualized the DNA helix . However, is there a seamless and contiguous appearance to these self- generated mental images? van Sommers surmised that the notion of imagery as being unified in a single topologically coherent display has not been empirically supported. van Sommers’ main support for the view of non-unitary topological mental imagery displays in the mind’s eye includes difficulties drawing complex designs (e.g., impossible objects such as the knot design) even when using simple and didactic line-by-line copying strategies .
parietal areas (Türe et al., 1999). Both egocentric and allocentric representations would then be both used during navigation (Burgess, 2006). Peculiar is also the increased activation observed in the right posterior part of the Lateral Sulcus and in right Subcentral Gyrus and Sulcus during allocentric rather than egocentric categorical judgments. The Lateral Sulcus separates the frontal and parietal lobes from the temporal lobe, whereas the Subcentral Gyrus, which may lie in the Lateral Sulcus (Petrides, 2014), is a U-shape gyrus that connects the pre- and postcentral gyri (Wagner et al., 2013). As far as we know, the Lateral Sulcus may contain, at least in monkeys, areas involved in spatial awareness and exploration (Grüsser et al., 1990; Chakraborty and Thier, 2000), whereas the Subcentral Gyrus is involved in the circuit of language (Gabrieli et al., 1998). This would suggest that these areas would specifically support attributions of verbal spatial categories (right-left) to external, not-body related, references. In fact, these areas are not present when egocentric and allocentric coordinate judgements are compared.