Functional Neural Networks Stratify Parkinson’s Disease Patients Across the Spectrum of Cognitive Impairment

Introduction: Cognitive impairment (CI) is a significant non-motor symptoms inParkinson’s disease (PD) that often precedes the emergence of motor symptoms by several years. Patients with PD hypothetically progress from stages without CI (PD-normal cognition [NC]) to stageswithMild CI (PD-MCI) and PDdementia (PDD). CI symptoms in PD are linked to different brain regions and neural pathways, in addition to being the result of dysfunctional subcortical regions. However, it is still unknown how functional dysregulation correlates to progression during the CI. Neuroimaging techniques hold promise in discriminating CI stages of PD and further contribute to the biomarker formation of CI in PD. In this study, we explore disparities in the clinical assessments and resting-state functional connectivity (FC) among three CI stages of PD. Methods: We enrolled 88 patients with PD and 26 healthy controls (HC) for a cross sectional clinical study and performed intra- and inter-network FC analysis in conjunction with comprehensive clinical cognitive assessment. Results: Our findings underscore the significance of several neural networks, namely, the default mode network (DMN), frontoparietal network (FPN), dorsal attention network, and visual network (VN) and their inter–intra-network FC in differentiating between PD-MCI and PDD. Additionally, our results showed the importance of sensory motor network, VN,DMN, and salience network (SN) in the discriminating PD-NC from PDD. Finally, in comparison to HC, we found DMN, FPN, VN, and SN as pivotal networks for further differential diagnosis of CI stages of PD. Conclusion:We propose that resting-state networks (RSN) can be a discriminating factor in distinguishing the CI stages of PD and progressing from PD-NC toMCI or PDD. The integration of clinical and neuroimaging data may enhance the early detection of PD in clinical settings and potentially prevent the disease from advancing to more severe stages

Lower prepulse inhibition in clinical high-risk groups but not in familial risk groups for psychosis compared with healthy controls

Aim Although the lower level of prepulse inhibition (PPI) of the startle response is well known in schizophrenia, the onset of this difference is not clear. The aim of the present study was to compare PPI in individuals with clinical and familial high risk for psychosis, and healthy controls. Methods We studied PPI in individuals within three groups: ultra-high risk for psychosis (UHR, n = 29), familial high risk for psychosis (FHR, n = 24) and healthy controls (HC, n = 28). The FHR group was chosen among siblings of patients with schizophrenia, whereas UHR was defined based on the Comprehensive Assessment of At-Risk Mental States (CAARMS). We collected clinical data using the BPRS-E, SANS and SAPS when individuals with UHR were antipsychotic-naive. A cognitive battery that assessed attention, cognitive flexibility, working memory, verbal learning and memory domains was applied to all participants. Results PPI was lower in the UHR group compared with both the FHR and HC groups. Those with a positive family history for schizophrenia had lower PPI than others in the UHR group. There was no difference in PPI between the FHR and HC groups. We found no relationship between PPI and cognitive performance in the three groups. Startle reactivity was not different among the three groups. Positive and negative symptoms were not related to PPI and startle reactivity in the UHR group. Conclusions Our findings suggest that clinical and familial high-risk groups for psychosis have different patterns of PPI

Implementation of low resolution electro-magnetic tomography with fMRI statistical maps on realistic head models

Functional neuroimaging studies can be performed by combining the modalities of fMRI and Electroencephalography because of their complementary properties. The main advantage of EEG imaging among other modalities is the high temporal resolution while fMRI has high spatial resolution. So, usage of these procedures is going to help us to gain more information about the functional organization of the brain. In this study, changes in the relationship between Steady State Visual Evoked Potentials (SSVEP) generators and BOLD responses during visual stimulation have been systematically studied with 5 stimulus presentation rates (2, 4, 6, 8, 10) between 2-10 Hz. fMRI Analysis was carried out using Statistical Parametric Mapping (SPM). The result of fMRI analysis is used as a localization mask for SSVEP localization process. SSVEP generators are localized using Low Resolution Electro Magnetic Tomography (LORETA) which is implemented on a realistic head model. Then, for each stimulus frequency voxel by voxel correlation values of the active regions are computed

Interactions of gamma and theta oscillations in the electroencephalogram (EEG) during memory processes

Human subjects typically keep about 7 +/- 2 items in short-term memory (STM). A theoretical neuronal model has been proposed to explain this phenomenon with physiological parameters of brain oscillations in the gamma and theta frequency range, i.e. roughly 30-80 and 4-8 Hz, respectively. In that model, STM capacity equals the number of gamma cycles (e.g. 25 ms for 40 Hz), which fit into one theta cycle (e.g. 166 ms for 6 Hz). The model is based on two assumptions: 1) theta activity should modulate gamma activity and 2) the theta/gamma ratio should correlate with human STM capacity. The first assumption is supported by electrophysiological data showing that the amplitude of gamma oscillations is modulated by the phase of theta activity. However, so far this has only been demonstrated for intracranial recordings. We analyzed human event-related EEG oscillations recorded in a memory experiment in which 13 subjects perceived known and unknown visual stimuli. The paradigm revealed event-related oscillations in the gamma range, which depended significantly on the phase of simultaneous theta activity. Our data are the first scalp-recorded human EEG recordings revealing a relationship between the gamma amplitude and the phase of theta oscillations, supporting the first assumption of the abovementioned theory. Interestingly, the involved frequencies revealed a 7:1 ratio. However, this ratio does not necessarily determine human STM capacity. Since such a correlation was not explicitly tested in our paradigm, our data is not conclusive about the second assumption. Instead of theta phase modulating gamma amplitude, it is also conceivable that focal gamma activity needs to be downsampled to theta activity, before it can interact with more distant brain regions

Genetic subtypes of human immunodeficiency virus type 1 (HIV-1) in Istanbul, Turkey

Background: Epidemiological surveillance of HIV-1 subtypes is an important and ongoing element of preparation for global antiviral interventions

Simultaneous EEG/fMRI Analysis of the Resonance Phenomena in Steady-State Visual Evoked Responses

The stability of the steady-state visual evoked potentials (SSVEPs) across trials and subjects makes them a suitable tool for the investigation of the visual system. The reproducible pattern of the frequency characteristics of SSVEPs shows a global amplitude maximum around 10 Hz and additional local maxima around 20 and 40 Hz, which have been argued to represent resonant behavior of damped neuronal oscillators

Simultaneous EEG/fMRI Analysis of the Resonance Phenomena in Steady-State Visual Evoked Responses

The stability of the steady-state visual evoked potentials (SSVEPs) across trials and subjects makes them a suitable tool for the investigation of the visual system. The reproducible pattern of the frequency characteristics of SSVEPs shows a global amplitude maximum around 10 Hz and additional local maxima around 20 and 40 Hz, which have been argued to represent resonant behavior of damped neuronal oscillators. Simultaneous electroencephalogram/functional magnetic resonance imaging (EEG/fMRI) measurement allows testing of the resonance hypothesis about the frequency-selective increases in SSVEP amplitudes in human subjects, because the total synaptic activity that is represented in the fMRI-Blood Oxygen Level Dependent (fMRI-BOLD) response would not increase but get synchronized at the resonance frequency. For this purpose, 40 healthy volunteers were visually stimulated with flickering light at systematically varying frequencies between 6 and 46 Hz, and the correlations between SSVEP amplitudes and the BOLD responses were computed. The SSVEP frequency characteristics of all subjects showed 3 frequency ranges with an amplitude maximum in each of them, which roughly correspond to alpha, beta and gamma bands of the EEG. The correlation maps between BOLD responses and SSVEP amplitude changes across the different stimulation frequencies within each frequency band showed no significant correlation in the alpha range, while significant correlations were obtained in the primary visual area for the beta and gamma bands. This non-linear relationship between the surface recorded SSVEP amplitudes and the BOLD responses of the visual cortex at stimulation frequencies around the alpha band supports the view that a resonance at the tuning frequency of the thalamo-cortical alpha oscillator in the visual system is responsible for the global amplitude maximum of the SSVEP around 10 Hz. Information gained from the SSVEP/fMRI analyses in the present study might be extrapolated to the EEG/fMRI analysis of the transient event-related potentials (ERPs) in terms of expecting more reliable and consistent correlations between EEG and fMRI responses, when the analyses are carried out on evoked or induced oscillations (spectral perturbations) in separate frequency bands instead of the time-domain ERP peaks