Automatic representation of a visual stimulus relative to a background in the right precuneus

Functional organization of the caudal part of the human superior parietal lobule

Like in macaque, the caudal portion of the human superior parietal lobule (SPL) plays a key role in a series of perceptive, visuomotor and somatosensory processes. Here, we review the functional properties of three separate portions of the caudal SPL, i.e., the posterior parieto-occipital sulcus (POs), the anterior POs, and the anterior part of the caudal SPL. We propose that the posterior POs is mainly dedicated to the analysis of visual motion cues useful for object motion detection during self-motion and for spatial navigation, while the more anterior parts are implicated in visuomotor control of limb actions. The anterior POs is mainly involved in using the spotlight of attention to guide reach-to-grasp hand movements, especially in dynamic environments. The anterior part of the caudal SPL plays a central role in visually guided locomotion, being implicated in controlling leg-related movements as well as the four limbs interaction with the environment, and in encoding egomotion-compatible optic flow. Together, these functions reveal how the caudal SPL is strongly implicated in skilled visually-guided behaviors.

Decreased utilization of allocentric coordinates during reaching movement in individuals with autism spectrum disorder

Despite numerous reports of abnormalities in limb motor controls in spatial orientation in individuals with autism spectrum disorder (ASD), the underlying mechanisms have not been elucidated. We studied the influence of allocentric coordinates on ongoing reaching movements, which has been reported to strongly affect the reaching movements of typically developing (TD) individuals. ASD and TD participants observed a target presented randomly on one of the four corners of a frame on a screen. After it disappeared, another frame was presented slightly shifted leftward/rightward. The participants touched the memorized position of the target relatively congruent with a reference frame (allocentric condition) or ignoring it (egocentric condition). Results suggested that TD individuals were apt to touch the positions in allocentric manner rather than egocentric manner, while ASDs did not show this prioritization. Our findings demonstrate that decreased utilization of visual landmarks in ongoing movement may underlie motor disabilities in autism.

Brain Functional Differences in Drug-Naive Major Depression with Anxiety Patients of Different Traditional Chinese Medicine Syndrome Patterns: A Resting-State fMRI Study

Major depressive disorder (MDD), especially combined with anxiety, has a high incidence and low detection rate in China. Literature has shown that patients under major depression with anxiety (MDA) are more likely to nominate a somatic, rather than psychological, symptom as their presenting complaint. In the theory of Traditional Chinese Medicine (TCM), clinical symptoms of MDD patients are mainly categorized into two different syndrome patterns: Deficiency and Excess. We intend to use resting-state functional magnetic resonance imaging (rs-fMRI) to investigate their brain functional differences and hopefully to find their brain function mechanism. For our research, 42 drug-naive MDA patients were divided into two groups (21 for Deficiency and 21 for Excess), with an additional 19 unaffected participants in the normal control (NC) group. We took Hamilton Depression Rating Scale (HAMD), Hamilton Anxiety Scale (HAMA), and brain fMRI scan for each group and analyzed the data. We first used Degree Centrality (DC) to map the functional differences in brain regions, utilized these regions as seed points, and used a seed-based functional connectivity (FC) analysis to identify the specific functional connection between groups. The Deficiency group was found to have higher HAMD scores, HAMA scores, and HAMD somatic factor than the Excess group. In the DC analysis, significant decreases were found in the right precuneus of both the Deficiency and Excess groups compared to the NC group. In the FC analysis, the right precuneus showed significant decreased network connectivity with the bilateral cuneus, as well as the right lingual gyrus in the Deficiency group when compared to the NC group and the Excess group. Through our research, it was found that precuneus dysfunction may have a relationship with MDA and Deficiency patients have more severe physical and emotional symptoms, and we realized that a larger sample size and multiple brain mode observations were needed in further research.

Automatic encoding of a target position relative to a natural scene

We previously showed that the brain automatically represents a target position for reaching relative to a large square in the background. In the present study, we tested whether a natural scene with many complex details serves as an effective background for representing a target. In the first experiment, we used upright and inverted pictures of a natural scene. A shift of pictures significantly attenuated prism adaptation of reaching movements as long as they were upright. In one-third of participants, adaptation was almost completely cancelled whether the pictures were upright or inverted. It was remarkable that there were two distinct groups of participants, one who relies fully on the allocentric coordinate and the other who depended only when the scene was upright. In the second experiment, we examined how long it takes for a novel upright scene to serve as a background. A shift of the novel scene had no significant effects when it was presented for 500 ms before presenting a target, but significant effects were recovered when presented for 1,500 ms. These results show that a natural scene serves as a background against which a target is automatically represented once we spend 1,500 ms in the scene.NEW & NOTEWORTHY Prism adaptation of reaching was attenuated by a shift of natural scenes as long as they were upright. In one-third of participants, adaptation was fully canceled whether the scene was upright or inverted. When an upright scene was novel, it took 1,500 ms to prepare the scene for allocentric coding. These results show that a natural scene serves as a background against which a target is automatically represented once we spend 1,500 ms in the scene.

Allocentric representations for target memory and reaching in human cortex

The use of allocentric cues for movement guidance is complex because it involves the integration of visual targets and independent landmarks and the conversion of this information into egocentric commands for action. Here, we focus on the mechanisms for encoding reach targets relative to visual landmarks in humans. First, we consider the behavioral results suggesting that both of these cues influence target memory, but are then transformed-at the first opportunity-into egocentric commands for action. We then consider the cortical mechanisms for these behaviors. We discuss different allocentric versus egocentric mechanisms for coding of target directional selectivity in memory (inferior temporal gyrus versus superior occipital gyrus) and distinguish these mechanisms from parieto-frontal activation for planning egocentric direction of actual reach movements. Then, we consider where and how the former allocentric representations of remembered reach targets are converted into the latter egocentric plans. In particular, our recent neuroimaging study suggests that four areas in the parietal and frontal cortex (right precuneus, bilateral dorsal premotor cortex, and right presupplementary area) participate in this allo-to-ego conversion. Finally, we provide a functional overview describing how and why egocentric and landmark-centered representations are segregated early in the visual system, but then reintegrated in the parieto-frontal cortex for action.

Altered spontaneous brain activity patterns in patients with retinal vein occlusion indicated by the amplitude of low-frequency fluctuation: A functional magnetic resonance imaging study

The aim of the present study was to explore the amplitude of low-frequency fluctuations (ALFF; a measurement of spontaneous brain activity) in different brain regions of patients with retinal vein occlusion (RVO) and its association with vision changes measurements. A total of 24 RVO patients (12 males and 12 females) and 24 healthy controls (HCs, 12 males and 12 females) were recruited, and they were closely matched regarding age, gender and education level (classified according to nine-year compulsory education in China and higher education, all including primary school, junior school, high school and university). ALFF values of different brain regions were gathered and analyzed, and statistical analysis software was used to explore the correlations between the average ALFF signals and clinical features. The ability of ALFF values to distinguish between subjects with RVO and HCs was analyzed by receiver operating characteristic (ROC) curves. The results indicated that the subjects from the RVO group had higher ALFF values than the HCs in the posterior lobe of the left cerebellum, inferior temporal gyrus, cerebellar anterior lobe, right cerebellum posterior/anterior lobe, and lower ALFF values in the medial frontal gyrus, right precuneus, left middle frontal gyrus, right angular gyrus and right superior frontal gyrus. The ROC curve analysis of each brain region indicated that the accuracy of the area under the ROC curves regarding the prediction of RVO was excellent. The best-corrected visual acuity (VA) in the left eye was positively correlated with the ALFF value of the right precuneus (r=0.767, P=0.004) and the best-corrected VA in the right eye was positively correlated with the ALFF value of the left middle frontal gyrus (r=0.935, P<0.001). The central subfield retinal thickness in the left eye was negatively correlated with the ALFF value of the right precuneus (r=−0.895; P<0.001). The duration of RVO in the right eye was positively correlated with the ALFF value of the left middle frontal gyrus (r=0.868; P<0.001). In conclusion, the present results indicate that RVO is associated with dysfunction of diverse brain regions, including language- and movement-associated areas, which may reflect the underlying pathogenic mechanisms of RVO (trial registry no. CDYFY-LL-2017025).

Neural substrates for allocentric-to-egocentric conversion of remembered reach targets in humans

Targets for goal-directed action can be encoded in allocentric coordinates (relative to another visual landmark), but it is not known how these are converted into egocentric commands for action. Here, we investigated this using a slow event-related fMRI paradigm, based on our previous behavioural finding that the allocentric-to-egocentric (Allo-Ego) conversion for reach is performed at the first possible opportunity. Participants were asked to remember (and eventually reach towards) the location of a briefly presented target relative to another visual landmark. After a first memory delay, participants were forewarned by a verbal instruction if the landmark would reappear at the same location (potentially allowing them to plan a reach following the auditory cue before the second delay), or at a different location where they had to wait for the final landmark to be presented before response, and then reach towards the remembered target location. As predicted, participants showed landmark-centred directional selectivity in occipital-temporal cortex during the first memory delay, and only developed egocentric directional selectivity in occipital-parietal cortex during the second delay for the 'Same cue' task, and during response for the 'Different cue' task. We then compared cortical activation between these two tasks at the times when the Allo-Ego conversion occurred, and found common activation in right precuneus, right presupplementary area and bilateral dorsal premotor cortex. These results confirm that the brain converts allocentric codes to egocentric plans at the first possible opportunity, and identify the four most likely candidate sites specific to the Allo-Ego transformation for reaches.

Cortical Activation during Landmark-Centered vs. Gaze-Centered Memory of Saccade Targets in the Human: An FMRI Study

A remembered saccade target could be encoded in egocentric coordinates such as gaze-centered, or relative to some external allocentric landmark that is independent of the target or gaze (landmark-centered). In comparison to egocentric mechanisms, very little is known about such a landmark-centered representation. Here, we used an event-related fMRI design to identify brain areas supporting these two types of spatial coding (i.e., landmark-centered vs. gaze-centered) for target memory during the Delay phase where only target location, not saccade direction, was specified. The paradigm included three tasks with identical display of visual stimuli but different auditory instructions: Landmark Saccade (remember target location relative to a visual landmark, independent of gaze), Control Saccade (remember original target location relative to gaze fixation, independent of the landmark), and a non-spatial control, Color Report (report target color). During the Delay phase, the Control and Landmark Saccade tasks activated overlapping areas in posterior parietal cortex (PPC) and frontal cortex as compared to the color control, but with higher activation in PPC for target coding in the Control Saccade task and higher activation in temporal and occipital cortex for target coding in Landmark Saccade task. Gaze-centered directional selectivity was observed in superior occipital gyrus and inferior occipital gyrus, whereas landmark-centered directional selectivity was observed in precuneus and midposterior intraparietal sulcus. During the Response phase after saccade direction was specified, the parietofrontal network in the left hemisphere showed higher activation for rightward than leftward saccades. Our results suggest that cortical activation for coding saccade target direction relative to a visual landmark differs from gaze-centered directional selectivity for target memory, from the mechanisms for other types of allocentric tasks, and from the directionally selective mechanisms for saccade planning and execution.

Modulation of Illusory Reversal in Tactile Temporal Order by the Phase of Posterior α Rhythm

The subjective temporal order of tactile stimuli, delivered sequentially to each hand with an interval of 100-300 ms, is often inverted when the arms are crossed. Based on data from behavioral and neuroimaging studies, it has been proposed that the reversal is due to a conflict between anatomical and spatial representations of the tactile signal or to the production of an inverted apparent motion signal. Because the α rhythms, which consist of a few distinct components, reportedly modulate tactile perception and apparent motion and serve as a 10 Hz timer, we hypothesized that the illusory reversal would be regulated by some of the α rhythms. To test this hypothesis, we conducted magnetoencephalographic recordings in both male and female participants during the tactile temporal order judgment task. We decomposed the α rhythms into five independent components and discovered that the illusory reversal was modulated by the phase of one independent component with strong current sources near the parieto-occipital (PO) sulcus (peri-PO component). As expected, the estimated current sources distributed over the human MST implicated to represent tactile apparent motion, in addition to the intraparietal region implicated in mapping tactile signals in space. However, the strongest source was located in the precuneus that occupies a central hub region in the cortical networks and receives tactile inputs through a tecto-thalamic pathway. These results suggest that the peri-PO component plays an essential role in regulating tactile temporal perception by modulating the thalamic nuclei that interconnect the superior colliculus with the cortical networks.SIGNIFICANCE STATEMENT Despite a long-held hypothesis that the posterior α rhythm serves as a 10 Hz timer that regulates human temporal perception, the contribution of the α rhythms in temporal perception is still unclear. We examined how the α rhythms influence tactile temporal order judgment. Judgment reversal depended on the phase of one particular α rhythm with its source near the parieto-occipital sulcus. The peri-parieto-occipital α rhythm may play a crucial role in organizing tactile temporal perception.

Short-latency allocentric control of saccadic eye movements

It is generally accepted that the neural circuits that are implicated in saccade control use retinotopically coded target locations. However, several studies have revealed that nonretinotopic representation is also used. This idea raises a question about whether nonretinotopic coding is egocentric (head or body centered) or allocentric (environment centered). In the current study, we hypothesized that allocentric coding may play a crucial role in immediate saccade control. To test this hypothesis, we used an immediate double-step saccade task toward two sequentially flashed targets with a frame in the background, and we examined whether the end point of the second saccade was affected by a transient shift of the background that participants were told to ignore. When the background was shifted transiently upward (or downward) during the flash of the second target, the second saccade generally erred the target downward (or upward), which was in the direction opposite to the shift of the background. The effect on the second saccade became significant within 150 ms after the frame was presented for decoding and was built up for 200 ms thereafter. When the second saccade was not adjusted, a small, corrective saccade followed within 300 ms. The effect scaled linearly with the shift size up to 3° for a noncorrective second saccade and up to 6° for a corrective saccade. The present results show that an allocentric location of a target is rapidly represented by the brain and used for controlling saccades.

NEW & NOTEWORTHY

We found that the saccade end point was shifted from the actual target position toward the direction expected from allocentric coding when a large frame in the background was transiently shifted during the period of target presentation. The effect occurred within 150 ms. The present study provides direct evidence that the brain rapidly uses allocentric coding of a target to control immediate saccades.

Gender differences in the neural response to acupuncture: clinical implications

OBJECTIVE

To examine gender differences and similarities in the psychophysical and brain responses to acupuncture at GB34, a point that is frequently used to treat motor function issues in Traditional Chinese Medicine.

METHODS

Functional MRI (fMRI) was used to measure brain activation in response to acupuncture at GB34 (on the right) in 19 healthy participants (9 male, 10 female). De qi sensations were rated to measure their psychophysical responses.

RESULTS

Overall de qi scores did not differ by gender, although females reported greater intensity of aching (p=0.04). Acupuncture activated the hippocampus, thalamus, globus pallidus, caudate body, claustrum, cingulate gyrus, and culmen in males, and the middle and inferior frontal gyrus, precuneus, postcentral gyrus, inferior parietal lobule, superior temporal gyrus, caudate body, insula, fusiform gyrus, cingulate gyrus, amygdala, and parahippocampal gyrus in females. The middle/medial frontal gyrus, middle temporal gyrus, thalamus, globus pallidus, caudate body, uvula, and cerebellar tonsil were activated when data from all subjects were combined. Relative to males, females exhibited greater brain activation in the right-sided postcentral gyrus, precentral gyrus, precuneus, postcentral gyrus, inferior parietal lobule, declive, middle occipital gyrus and parahippocampal gyrus.

CONCLUSIONS

The neural effects of GB34 acupuncture might differ between males and females because different brain structures were modulated in response to acupuncture. This potential gender effect should be taken into account in future clinical research. We also revealed that the caudate body was activated by GB34 acupuncture in both males and females and may represent a major target of GB34 acupuncture.

TRIAL REGISTRATION NUMBER

KMC IRB 0861-06.