Simone Gazzellini

Test-retest reliability of graph metrics of resting state MRI functional brain networks: A review.

The employment of graph theory to analyze spontaneous fluctuations in resting state BOLD fMRI data has become a dominant theme in brain imaging studies and neuroscience. Analysis of resting state functional brain networks based on graph theory has proven to be a powerful tool to quantitatively characterize functional architecture of the brain and it has provided a new platform to explore the overall structure of local and global functional connectivity in the brain. Due to its increased use and possible expansion to clinical use, it is essential that the reliability of such a technique is very strongly assessed. In this review, we explore the outcome of recent studies in network reliability which apply graph theory to analyze connectome resting state networks. Therefore, we investigate which preprocessing steps may affect reproducibility the most. In order to investigate network reliability, we compared the test-retest (TRT) reliability of functional data of published neuroimaging studies with different preprocessing steps. In particular we tested influence of global signal regression, correlation metric choice, binary versus weighted link definition, frequency band selection and length of time-series. Statistical analysis shows that only frequency band selection and length of time-series seem to affect TRT reliability. Our results highlight the importance of the choice of the preprocessing steps to achieve more reproducible measurements.

Brain network involved in visual processing of movement stimuli used in upper limb robotic training: an fMRI study.

BackgroundThe potential of robot-mediated therapy and virtual reality in neurorehabilitation is becoming of increasing importance. However, there is limited information, using neuroimaging, on the neural networks involved in training with these technologies. This study was intended to detect the brain network involved in the visual processing of movement during robotic training. The main aim was to investigate the existence of a common cerebral network able to assimilate biological (human upper limb) and non-biological (abstract object) movements, hence testing the suitability of the visual non-biological feedback provided by the InMotion2 Robot.MethodsA visual functional Magnetic Resonance Imaging (fMRI) task was administered to 22 healthy subjects. The task required observation and retrieval of motor gestures and of the visual feedback used in robotic training. Functional activations of both biological and non-biological movements were examined to identify areas activated in both conditions, along with differential activity in upper limb vs. abstract object trials. Control of response was also tested by administering trials with congruent and incongruent reaching movements.ResultsThe observation of upper limb and abstract object movements elicited similar patterns of activations according to a caudo-rostral pathway for the visual processing of movements (including specific areas of the occipital, temporal, parietal, and frontal lobes). Similarly, overlapping activations were found for the subsequent retrieval of the observed movement. Furthermore, activations of frontal cortical areas were associated with congruent trials more than with the incongruent ones.ConclusionsThis study identified the neural pathway associated with visual processing of movement stimuli used in upper limb robot-mediated training and investigated the brain’s ability to assimilate abstract object movements with human motor gestures. In both conditions, activations were elicited in cerebral areas involved in visual perception, sensory integration, recognition of movement, re-mapping on the somatosensory and motor cortex, storage in memory, and response control. Results from the congruent vs. incongruent trials revealed greater activity for the former condition than the latter in a network including cingulate cortex, right inferior and middle frontal gyrus that are involved in the go-signal and in decision control. Results on healthy subjects would suggest the appropriateness of an abstract visual feedback provided during motor training. The task contributes to highlight the potential of fMRI in improving the understanding of visual motor processes and may also be useful in detecting brain reorganisation during training.

Functional and Gait Assessment in Children and Adolescents Affected by Friedreich's Ataxia: A One-Year Longitudinal Study.

Friedreich’s ataxia is the most common autosomal recessive form of neurodegenerative ataxia. We present a longitudinal study on the gait pattern of children and adolescents affected by Friedreich’s ataxia using Gait Analysis and the Scale for the Assessment and Rating of Ataxia (SARA). We assessed the spectrum of changes over 12 months of the gait characteristics and the relationship between clinical and instrumental evaluations. We enrolled 11 genetically confirmed patients affected by Friedreich’s ataxia in this study together with 13 normally developing age-matched subjects. Eight patients completed a 12-month follow-up under the same protocol. By comparing the gait parameters of Friedreich’s ataxia with the control group, we found significant differences for some relevant indexes. In particular, the increased knee and ankle extension in stance revealed a peculiar biomechanical pattern, which correlated reliably with SARA Total, Gait and Sitting scores. The knee pattern showed its consistency also at the follow-up: Knee extension increased from 6.8±3.5° to -0.5±3.7° and was significantly correlated with the SARA total score. This feature anticipated the loss of the locomotor function in two patients. In conclusion, our findings demonstrate that the selective and segmental analysis of kinetic/kinematic features of ataxic gait, in particular the behavior of the knee, provides sensitive measures to detect specific longitudinal and functional alterations, more than the SARA scale, which however has proved to be a reliable and practical assessment tool. Functional outcomes measures integrated by instrumental evaluation increase their sensitivity, reliability and suitability for the follow-up of the disease progression and for the application in clinical trials and in rehabilitative programs.

The impact of vision on the dynamic characteristics of the gait: strategies in children with blindness

Visually impaired persons present an atypical gait pattern characterized by slower walking speed, shorter stride length and longer time of stance. Three explanatory hypotheses have been advanced in the literature: balance deficit, lack of an anticipatory mechanisms and foot probing the ground. In the present study, we compared the three hypotheses by applying their predictions to gait analysis and posturography of blind children without neurological impairment and compared their performance with that of an age-matched control group. The gait analysis results documented that blind children presented reduced walking velocity and step length, increased step width and external rotation of the foot progression angle, reduced ground reaction force and ankle maximum angle, moment and power in late stance, increased head flexion, decreased thorax flexion and pelvis anteversion, compared with the control group. The posturographic analysis showed equal skill level between blind children and normally sighted children when they close their eyes. The results are consistent with only one of the three hypotheses: namely, they prove that blind children’s gait is influenced only by the absence of visually driven anticipatory control mechanisms. Finally, rehabilitative recommendations for children with blindness are advanced in discussion.

Developmental lag of visuospatial attention in Duchenne muscular dystrophy

Children with Duchenne muscular dystrophy (DMD) present a specific deficit of voluntary attention but to date there has been no clear characterization of their attentional skills. The present study investigated the hypothesis that DMD patients present deficits of both voluntary and automatic visuospatial attention systems and that their performance could be equivalent to that of younger healthy males. Twenty males (mean age 10 years) with diagnosis of DMD, 20 age-matched healthy males (10 years 3 months) and 20 healthy younger males (7 years 6 months) were required to perform two visuospatial attention tasks: voluntary and automatic. In the voluntary task, the performance of the DMD group was significantly worse than that of the age-matched group, and equal to that of the younger controls. In the automatic attention task also, the performance of the DMD patients was less efficient than that of the age-matched controls and equal to that of the younger children. This study supports the previous report of voluntary attention deficit in DMD and extends the evidence to include also an automatic attention system deficit. The development level of attention in DMD patients is below that expected for their age and corresponds to a delay of about three years.

Time–frequency analyses of reaction times and theta/beta EEG ratio in pediatric patients with traumatic brain injury: A preliminary study

ABSTRACT Purpose: The literature on patients with attention deficit reports peculiar reaction time (RT) oscillation at very low frequencies (VLFO=0.06–0.2 Hz). The data were explained as default mode network (DMN) intrusion in goal-oriented activity. The present study investigates whether a pattern of recurrent lapses in attention can be detected in TBI patients and whether VLFO can be generalized to the sustained attention deficit, regardless of etiology. Methods: Groups of pediatric TBIs and healthy controls performed four attentional tasks. RT and theta/beta timeseries were subjected to wavelet analyses. Results: Significant high-power VLFOs were recorded in patient group performances but not in those of controls, both for RTs and theta/beta in all the tasks. Conclusion: This preliminary study suggests that central-midline theta/beta ratio could be considered a neurophysiological correlate of RT variability and that the general continuous goal-oriented activity can be cross-etiologically affected by recurrent lapses in attention regardless of the specific cognitive component involved.

Association between Attention and Heart Rate Fluctuations in Pathological Worriers

Recent data suggests that several psychopathological conditions are associated with alterations in the variability of behavioral and physiological responses. Pathological worry, defined as the cognitive representation of a potential threat, has been associated with reduced variability of heart beat oscillations (i.e., decreased heart rate variability; HRV) and lapses of attention indexed by reaction times (RTs). Clinical populations with attention deficit show RTs oscillation around 0.05 and 0.01 Hz when performing a sustained attention task. We tested the hypothesis that people who are prone to worry do it in a predictable oscillating pattern revealed through recurrent lapses in attention and concomitant oscillating HRV. Sixty healthy young adults (50% women) were recruited: 30 exceeded the clinical cut-off on the Penn State Worry Questionnaire (PSWQ; High-Worry, HW); the remaining 30 constituted the Low-Worry (LW) group. After a diagnostic assessment, participants performed two 15-min sustained attention tasks, interspersed by a standardized worry-induction procedure. RTs, HRV and moods were assessed. The analyses of the frequency spectrum showed that the HW group presents a significant higher and constant peak of RTs oscillation around 0.01 Hz (period 100 s) after the induction of worry, in comparison with their baseline and with the LW group that was not responsive to the induction procedure. Physiologically, the induction significantly reduced high-frequency HRV and such reduction was associated with levels of self-reported worry. Results are coherent with the oscillatory nature of the default mode network (DMN) and further confirm an association between cognitive rigidity and autonomic nervous system inflexibility.

Time to boundary function to assess upright stance in blind children

The goal of this preliminary study was to assess the difference in postural stability between blind and sighted children using the Time to Boundary function (TtB). The experiment was conducted in twelve children (6-12 yrs), six of them had no visual impairment, and other six had congenital blindness. The participants stood on RotoBit force plate maintaining upright stance in static conditions. Each blind subject executed the task three times, each sighted subject executed the task six times, three with eyes closed (EC) and three with eyes open (EO). For all subjects each repetition lasted 30 s. The Centre of Pressure (CoP) coordinates, extracted directly from a force plate, are used to calculate four classical parameters (sway path, sway area, mean amplitude and mean frequency) and a predictive variable called Time to Boundary (TtB). The latter is the time it would take the CoP, given its instantaneous trajectory, to contact a stability boundary. Descriptive statistics were calculated for all parameters. Twoway ANOVA test was done considering the visual condition (EO, EC, BLIND) and the repetitions (RP) as a factor. In the first comparison (BLIND/EO) the results showed significant difference for all the parameters except for TtB. In the second comparison (BLIND/EC) the results showed significant difference only for TtB. In the third comparison (EO/EC) the results showed significant difference for all the calculated parameters. Therefore the TtB would be used to asses the postural control in children with blindness.