Brain

Is schizotypic maternal personality linked to sensory gating abilities during infancy? Abstract Schizotypy is a personality dimension within the general population elevated among schizophrenia-spectrum patients and their first-degree relatives. Sensory gating is the pre-attentional habituation of responses distinguishing between important and irrelevant information. This is measured by event-related potentials, which have been found to display abnormalities in schizophrenic disorders. The current study investigated whether 6-month-old infants of mothers with schizotypic traits display sensory gating abnormalities. The paired-tone paradigm: two identical auditory tones (stimulus 1 and stimulus 2) played 500 ms apart, was used to probe the selective activation of the brain during 15-minutes of sleep. Their mothers completed the Oxford and Liverpool Inventory of Feelings and Experiences-Short Form as an index of schizotypy dimensionality, categorized into: infants of control, and infants of schizotypic, mothers. The findings revealed that although the infants' P50 components displayed significant differences between stimulus 1 and stimulus 2 in the paired-tone paradigm, there was no clear difference between infants of schizotypic and infants of control mothers. In contrast, all mothers displayed significant differences between stimulus 1 and stimulus 2, as observed in the infants, but also significant differences between their sensory gating ability correlated with schizotypy dimensionality. These findings are consistent with sensory processes, such as sensory gating, evidencing impairment in schizophrenia-spectrum disorders. The present research supports the idea that first-degree relatives of individuals who identify on this spectrum, within the sub-clinical category, do not display the same deficit at 6 postnatal months of age.

Referent control of anticipatory grip force during reaching in stroke: an experimental and modeling study Abstract To evaluate normal and impaired control of anticipatory grip force (GF) modulation, we compared GF production during horizontal arm movements in healthy and post-stroke subjects, and, based on a physiologically feasible dynamic model, determined referent control variables underlying the GF–arm motion coordination in each group. 63% of 13 healthy and 48% of 13 stroke subjects produced low sustained initial force (< 10 N) and increased GF prior to arm movement. Movement-related GF increases were higher during fast compared to self-paced arm extension movements only in the healthy group. Differences in the patterns of anticipatory GF increases before the arm movement onset between groups occurred during fast extension arm movement only. In the stroke group, longer delays between the onset of GF change and elbow motion were related to clinical upper limb deficits. Simulations showed that GFs could emerge from the difference between the actual and the referent hand aperture (Ra) specified by the CNS. Similarly, arm movement could result from changes in the referent elbow position (Re) and could be affected by the co-activation (C) command. A subgroup of stroke subjects, who increased GF before arm movement, could specify different patterns of the referent variables while reproducing the healthy typical pattern of GF–arm coordination. Stroke subjects, who increased GF after arm movement onset, also used different referent strategies than controls. Thus, altered anticipatory GF behavior in stroke subjects may be explained by deficits in referent control.

Control strategies for rapid, visually guided adjustments of the foot during continuous walking Abstract When walking over stable, complex terrain, visual information about an upcoming foothold is primarily utilized during the preceding step to organize a nearly ballistic forward movement of the body. However, it is often necessary to respond to changes in the position of an intended foothold that occur around step initiation. Although humans are capable of rapidly adjusting foot trajectory mid-swing in response to a perturbation of target position, such movements may disrupt the efficiency and stability of the gait cycle. In the present study, we consider whether walkers sometimes adopt alternative strategies for responding to perturbations that interfere less with ongoing forward locomotion. Subjects walked along a path of irregularly spaced stepping targets projected onto the ground, while their movements were recorded by a full-body motion-capture system. On a subset of trials, the location of one target was perturbed in either a medial–lateral or anterior–posterior direction. We found that subjects were best able to respond to perturbations that occurred during the latter half of the preceding step and that responses to perturbations that occurred during a step were less successful than previously reported in studies using a single-step paradigm. We also found that, when possible, subjects adjusted the ballistic movement of their center of mass in response to perturbations. We conclude that, during continuous walking, strategies for responding to perturbations that rely on reach-like movements of the foot may be less effective than previously assumed. For perturbations that are detected around step initiation, walkers prefer to adapt by tailoring the global, pendular mechanics of the body.

Effect of coadministration of the GABA B agonist baclofen and the 5-HT 2C agonist Ro60-0175 on the expression of amphetamine-induced locomotor sensitization Abstract GABAB and 5-HT2C agonists are effective in attenuating the behavioral effects of psychostimulants. However, they induce adverse side effects when used in high doses. The previous evidence has suggested that the 5HT2C receptor activation effect could be produced by an increased release of GABA in the ventral tegmental area (VTA) and the consequent activation of GABAergic receptors. Therefore, the objective of this study was to evaluate the effects of joint administration of an intermediate dose of the GABAB agonist baclofen (3.0 mg/kg) with different doses of the 5HT2C agonist Ro60-0175 (0.3, 1.0, and 3.0 mg/kg) on the locomotor sensitization expression induced by the repeated administration of amphetamine (1.0 mg/kg). Our results showed an attenuation of the expression of sensitization in a dose-dependent manner with both agonists. In both cases, we observed a complete blockade at the highest dose. In addition, the intermediate dose of baclofen increased the effects of the three doses of Ro60-0175. These results support the role of the joint action of GABAB and 5-HT2C receptors in the effects of psychostimulants. However, it remains to be explored whether the observed effect can be attributed to receptors located in the VTA or the nucleus accumbens.

Divergent effects of conditioned pain modulation on subjective pain and nociceptive-related brain activity Abstract Background and objectives Pain is a complex experience involving both nociceptive and affective–cognitive mechanisms. The present study evaluated whether modulation of pain perception, employing a conditioned pain modulation (CPM) paradigm, is paralleled by changes in contact heat-evoked potentials (CHEPs), a brain response to nociceptive stimuli. Methods Participants were 25 healthy, pain-free, college students (12 males, 13 females, mean age 19.24 ± 0.97 years). Twenty computer-controlled heat stimuli were delivered to the non-dominant forearm and CHEPs were recorded at Cz using a 32-channel EEG system. After each stimulus, participants rated the intensity of the heat pain using the 0–100 numerical rating scale. The latency and amplitude of N2, P2 components as well as single-sweep spectral analysis of individual CHEPs were measured offline. For CPM, participants had to submerge their dominant foot into a neutral (32 °C) or noxious (0 °C) water bath. CHEPs and heat pain ratings were recorded in 3 different conditions: without CPM, after neutral CPM (32 °C) and after noxious CPM (0 °C). Results The noxious CPM induced a facilitatory pain response (p = 0.001) with an increase in heat pain following noxious CPM compared to neutral CPM (p = 0.001) and no CPM (p = 0.001). Changes in CHEPs did not differ between conditions when measured as N2–P2 peak-to-peak amplitude (p = 0.33) but the CPM significantly suppressed the CHEPs-related delta power (p = 0.03). Changes in heat pain in the noxious CPM were predicted by trait catastrophizing variables (p = 0.04). Conclusion The current study revealed that pain facilitatory CPM is related to suppression of CHEPs delta power which could be related to dissociation between brain responses to noxious heat and pain perception.

How does environmental knowledge allow us to come back home? Abstract Herein, we investigate how the three types of mental spatial representation (landmark, route and survey) are reorganized to perform wayfinding and homing behaviour. We also investigate the contribution of visuo-spatial working memory in reaching and in vista space in performing the retracing of the path. For this purpose, we asked 68 healthy college students to learn and come back along an unknown path in a real environment and to perform two different forward and backward working memory tasks, one in the reaching space (Corsi Block-Tapping Test) and the other in a vista space (Walking Corsi Test). The results show that participants performed better when travelling the route forward (which corresponds to the originally learned direction) than when travelling the route backward (return path) and that working memory in vista space is crucial for both wayfinding and homing behaviour, while the working memory for reaching space contributes only to homing behaviour. Although homing behaviour is an early mechanism in navigation shared among many species, it represents a very complex behaviour that requires both topographic and visuo-spatial memory as well as the first two levels of environmental knowledge.

Transcranial alternating current stimulation over the prefrontal cortex enhances episodic memory recognition Abstract It remains unknown whether transcranial alternating current stimulation (tACS) affects episodic memory and the effect of gamma oscillations delivered to the left prefrontal cortex (PFC) on long-term memory retention has not been fully investigated. We examined whether tACS over the left PFC enhances recognition of episodic memory. The study enrolled 36 healthy young adult volunteers. The participants were randomly assigned to either a tACS group [n = 18; 14 females; mean age ± standard deviation (SD): 21.2 ± 0.4 years] or a sham-control group [n = 18; 14 females; mean age ± SD: 21.2 ± 0.4 years]. Participants received either tACS or sham stimulation both during the learning task that was conducted on day 1 and during a recognition task on day 2. The recognition task was also conducted on days 1 and 7, and response accuracy was measured at all three time points (days 1, 2, and 7). Patients in the tACS group were better able to retain long-term memory than those in the sham-control group. These findings suggest that tACS over the left PFC enhances recognition of episodic memory in healthy young adults.

Neuromechanical control of leg length and orientation in children and adults during single-leg hopping Abstract Adult-like fine control of cyclical motor patterns found in locomotion develops into adolescence. Single-leg hopping in place is one such motor pattern where children have demonstrated a reduced capacity to control horizontal motion and match metronome cues. These developmental differences might arise from immature inter-segment coordination strategies and variability regulation. Therefore, the purpose of this study was to use an uncontrolled manifold (UCM) analysis to evaluate the control of segment angle variance (i.e., local variables) to stabilize leg length and leg orientation (i.e., task variables) in the sagittal plane between young adults and children aged 5–11 years old while hopping at different frequencies. The UCM space and its orthogonal space were constructed and segment angle variance was partitioned into these two spaces. Increased variance in the UCM space represents the stabilization of a task variable, while increased variance in its orthogonal space indicates a greater deviation of a task variable from its mean value. Our results indicated that children have developed an adult-like inter-segment coordination strategy of stabilizing leg length at mid-stance and leg orientation during flight. However, children might have an underdeveloped capacity to modulate leg length at take-off from cycle-to-cycle. Moreover, when increasing hopping frequency, children showed limited capacity to selectively increase leg-length stabilization. When decreasing hopping frequency, children illustrated an increased stabilization of leg orientation over the entire stance phase. Mid-stance leg-length stabilization might emerge with the motor skill; however, other inter-segment coordination strategies might continue to develop beyond 11-years of age.

Remote muscle contraction enhances spinal reflexes in multiple lower-limb muscles elicited by transcutaneous spinal cord stimulation Abstract Transcutaneous spinal cord stimulation (tSCS) is a useful technique for the clinical assessment of neurological disorders. However, the characteristics of the spinal cord circuits activated by tSCS are not yet fully understood. In this study, we examined whether remote muscle contraction enhances the spinal reflexes evoked by tSCS in multiple lower-limb muscles. Eight healthy men participated in the current experiment, which required them to grip a dynamometer as fast as possible after the presentation of an auditory cue. Spinal reflexes were evoked in multiple lower-limb muscles with different time intervals (50–400 ms) after the auditory signals. The amplitudes of the spinal reflexes in all the recorded leg muscles significantly increased at 50–250 ms after remote muscle activation onset. This suggests that remote muscle contraction simultaneously facilitates the spinal reflexes in multiple lower-limb muscles. In addition, eight healthy men performed five different tasks (i.e., rest, hand grip, pinch grip, elbow flexion, and shoulder flexion). Compared to control values recorded just before each task, the spinal reflexes evoked at 250 ms after the auditory signals were significantly enhanced by the above tasks except for the rest task. This indicates that such facilitatory effects are also induced by remote muscle contractions in different upper-limb areas. The present results demonstrate the existence of a neural interaction between remote upper-limb muscles and spinal reflex circuits activated by tSCS in multiple lower-limb muscles. The combination of tSCS and remote muscle contraction may be useful for the neurological examination of spinal cord circuits.

Force asymmetry deteriorates complementary force production during joint action Abstract The present study aimed to determine the effects of force asymmetry on interpersonal force production. This study consisted of an individual task executed by one participant at a time in a pair, and three joint tasks executed by two participants simultaneously under conditions of 1:1, 1:0.75, and 1:0.5. Two individuals produced discrete forces at the same time so that the sum of forces they produced was the target force in the joint task. Under the 1:1 condition, the target force was the sum of the maximum voluntary contraction (MVC) produced by the index finger of each participant × 0.1 (10% MVC). Under the 1:0.75 condition, the investigators manipulated the force produced by only one of the pair, for example, B, but not A. The feedback was also scaled as a result. The target force was the MVC of participant A + the MVC of participant B × 0.75 × 0.1. Similarly, the target force under the 1:0.5 condition was the MVC of participant A + the MVC of participant B × 0.5 × 0.1. The present study found that forces produced by pairs were negatively correlated and the correlation value was higher under the 1:1 condition than the 1:0.75 and 1:0.5 conditions. The absolute error was smaller under the 1:1 condition than the 1:0.5 condition. Complementary force production was attenuated and the error increased as differences between forces produced by two participants increased. Thus, asymmetry of forces produced by pairs deteriorated complementary force production and interpersonal performance.

Alexandros Sfakianakis
Anapafseos 5 . Agios Nikolaos
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alsfakia@gmail.com