Clarifying the functional process represented by reduced P50 suppression in schizophrenia

P50 suppression is a measure of the brain’s ability to modulate its response to incoming repetitive auditory stimuli that is derived from the electroencephalogram. This measure is widely used in psychiatric research and is argued to be a schizophrenia endophenotype. However, inconsistent results within this literature suggest that P50 suppression, even in healthy populations, is poorly understood and limits the ‘endophenotype’ claim. An understanding of methodological issues relevant to P50 suppression measurement, variables influencing P50 suppression, and the neural function it indexes in healthy subjects will inform psychiatric research as to the nature of impairments observed in schizophrenia

An evaluation of P50 suppression methodologies

\u27P50 suppression\u27, an index of sensory gating, has demonstrated utility in schizophrenia research. It is widely reported that P50 suppression is deficient in schizophrenia patients and an endophenotypic marker for the disorder. However, unresolved methodological issues including the unestablished reliability of the measure, unknown effects of time-on-task and long protocol undermine its usefulness. In order to address these methodological issues, twenty healthy participants\u27 P50 suppression was measured in a long P50 paradigm. This enabled the measurement of within-session reliability, temporal course of P50 suppression, and effects of the inter-pair interval parameter. Results indicated good within-session reliability for P50 suppression (ICC = .668); changes in P50 suppression across the session (a 31% increase over the 78 minute recording); and comparable P50 suppression at long (9 s) and short (3 s) inter-pair intervals. It is concluded that given appropriate conditions, P50 suppression can be measured reliably within-session. Further, time-on-task effects need to be taken into account when measuring P50 suppression in a long paradigm or calculating reliability. Lastly, the inter-pair interval can be substantially shortened in studies with healthy participants allowing for an appreciable reduction in P50 suppression recording time

Can explicit suggestions about the harmfulness of EMF exposure exacerbate a nocebo response in healthy controls?

2018 Elsevier Inc. While there has been consistent evidence that symptoms reported by individuals who suffer from Idiopathic Environmental Intolerance attributed to Electromagnetic Fields (IEI-EMF) are not caused by EMF and are more closely associated with a nocebo effect, whether this response is specific to IEI-EMF sufferers and what triggers it, remains unclear. The present experiment tested whether perceived EMF exposure could elicit symptoms in healthy participants, and whether viewing an \u27alarmist\u27 video could exacerbate a nocebo response. Participants were randomly assigned to watch either an alarmist (N = 22) or control video (N = 22) before completing a series of sham and active radiofrequency (RF) EMF exposure provocation trials (2 open-label, followed by 12 randomized, double-blind, counterbalanced trials). Pre- and post-video state anxiety and risk perception, as well as belief of exposure and symptom ratings during the open-label and double-blind provocation trials, were assessed. Symptoms were higher in the open-label RF-ON than RF-OFF trial (p \u3c.001). No difference in either symptoms (p =.183) or belief of exposure (p =.144) was observed in the double-blind trials. Participants who viewed the alarmist video had a significant increase in symptoms (p =.041), state anxiety (p \u3c.01) and risk perception (p \u3c.001) relative to the control group. These results reveal the crucial role of awareness and belief in the presentation of symptoms during perceived exposure to EMF, showing that healthy participants exhibit a nocebo response, and that alarmist media reports emphasizing adverse effects of EMF also contribute to a nocebo response

Pulse modulated radiofrequency exposure influences cognitive performance

Purpose: To investigate whether exposure to pulse modulated radiofrequency (PM RF) influences human cognitive performance, and whether it does so in a dose-dependent manner. Materials and methods: Thirty-six healthy adults participated in a randomized, double-blind, counterbalanced provocation study. Cognitive performance was assessed using a visual discrimination task and a modified Sternberg working memory task, which were calibrated to individual performance levels in a preliminary testing session. An sXh920 planar exposure system was used to generate a 920 MHz GSM-like signal, providing three conditions (peak-spatial SAR averaged over 10 g) of 0 W/kg (sham), 1 W/kg (low RF) and 2 W/kg (high RF). Results: A significant decrease in reaction time (RT) in the Sternberg working memory task was found during exposure compared to sham. This effect was not dose-dependent. Conclusions: Cognitive performance was shown to be faster under PM RF conditions, relative to sham, in a working memory task. While the majority of the literature has not found effects of PM RF exposure on cognitive performance, it is possible that the methodological improvements employed in the present study increased sensitivity, and thus the ability to detect potential effects

Clarifying the functional process represented by P50 suppression

P50 suppression refers to the amplitude-reduction of the P50 event related potential to the second (S2) relative to the first (S1) of identical auditory stimuli presented 500. ms apart. Theory suggests that refractory periods (RPs) and/or inhibitory inputs (II) underlie P50 suppression. The present study manipulated interval between stimulus pairs (IPI: 2, 8. s) and direction of participants\u27 attention (Attention, Non-Attention) in order to determine which theory best explains P50 suppression. The rationale is that: 1/ RP and II predict opposite effects of manipulating the functionality of the mechanism responsible for S2P50 suppression (e.g. reducing function would increase S2P50 according to the II and decrease S2P50 according to the RP hypothesis); 2/ IPI2 (relative to IPI8) will reduce functionality of the mechanism responsible for S2P50 suppression, as it results in less recovery of (and a greater challenge to) that mechanism - RP would thus predict reduced S2P50, whereas II would predict enhanced S2P50 amplitude; and 3/ where the mechanism responsible for S2P50 suppression is challenged (i.e. at IPI2, due to insufficient recovery), Attention (relative to Non-Attention) will enhance functionality of this mechanism - RP would thus predict increased S2P50, whereas II would predict reduced S2P50 amplitude. In the Non-Attention paradigm, reducing IPI from 8 to 2. s tended to increase S2P50 amplitude (and consequently impaired P50 suppression), and in the 2. s IPI paradigm, directing attention towards the stimuli reduced S2P50 amplitude (and improved P50 suppression), with both effects supporting the II hypothesis only

Does acute radio-frequency electromagnetic field exposure affect visual event-related potentials in healthy adults?

Objective: To use improved methods to address the question of whether acute exposure to radio-frequency (RF) electromagnetic fields (RF-EMF) affects early (80-200 ms) sensory and later (180-600 ms) cognitive processes as indexed by event-related potentials (ERPs). Methods: Thirty-six healthy subjects completed a visual discrimination task during concurrent exposure to a Global System for Mobile Communications (GSM)-like, 920 MHz signal with peak-spatial specific absorption rate for 10 g of tissue of 0 W/kg of body mass (Sham), 1 W/kg (Low RF) and 2 W/kg (High RF). A fully randomised, counterbalanced, double-blind design was used. Results: P1 amplitude was reduced (p =.02) and anterior N1 latency was increased (p =.04) during Exposure compared to Sham. There were no effects on any other ERP latencies or amplitudes. Conclusions: RF-EMF exposure may affect early perceptual (P1) and preparatory motor (anterior N1) processes. However, only two ERP indices, out of 56 comparisons, were observed to differ between RF-EMF exposure and Sham, suggesting that these observations may be due to chance. Significance: These observations are consistent with previous findings that RF-EMF exposure has no reliable impact on cognition (e.g., accuracy and response speed)