By Ovidiu C. Banea
Neurophysiologic measurements will be performed in three groups: healthy-control group (HS), treatment group (TG) and patient-control group (CG) (at the beginning of the study – baseline or T1, after the treatment T2, one month after the treatment T3 and 3 months after the treatment T4).
Reductions in power or synchrony of evoked gamma oscillations have been reported in chronic, first episode and early-onset schizophrenia. Associations between aspects of reduced gamma activity and severity of specific symptoms in patients with chronic schizophrenia have been reported, but the specificity and reproducibility of these findings remain to be established (Williams 2010).
Quantitative EEG or QEEG is a test and mathematical processing of digitally acquired EEG which permits the conversion of the brainwaves to digital form to allow for comparison between neurologically normative and dysfunctional individuals (Kropotov 2010). Several QEEG techniques, commonly called “EEG brain mapping,” include topographic displays of voltage or frequency, statistical comparisons to normative values, and discriminant analysis (Nuwer 1997). There is interest in using qEEG as a clinical biomarker to assist in the diagnosis of Alzheimer’s disease, Attention deficit hyperactivity disorder (ADHD), schizophrenia, and traumatic brain injury (TBI). Current projects include researching the reproducibility of the power spectral density bands to help validate qEEG as a clinical biomarker (FDA, 2018). In our study, we will use the conventional 10-20 EEG setting to acquire brain activity. We will use dense-array EEG (dEEG) for a better spatial sampling density. Biophysical analyses will be obtained with an intersensor distance of one to two cm. We will measure the Event-related potentials directly from the channels especially designed.
Method
Subjects fulfilling the inclusion and exclusion criteria will be asked to sign an informal consent and a 3 minutes spontaneous resting EEG will be recorded between 09.00 and 12.00 h on the day of their admission (Mitra et al. 2015).
Brain activity will be recorded by using waveguard original EEG cap (ANT Neuro, Netherlands) with high-density 256 channels during T1 and T2 scheduled timings and with 64 channels at T3 and T4 timings (Figure 1) in a resting state condition with closed eyes (sampling rate = 512 Hz, A/D conversion = 24-bit). Data will be stored and analyzed offline using the MATLAB based EEGLAB toolbox as well as the Statistical Analysis. The EEG will be referenced off-line to the common average potential and filtered between 0.5 and 70 Hz. Additionally, the signal will be filtered using the 48−52 Hz stop-band Notch filter. Fast Fourier Transformation will be used to determine spectral power in the gamma frequency range, separated into low gamma (31−48 Hz) and high gamma (52−70 Hz) bands. The relative power, will be computed and included to statistical analyses (Nuwer 1997; Baradits et al. 2016).
The event-related potentials are EEG changes that are time locked to sensory, motor or cognitive events. ERPs provide safe and noninvasive approach to study psychophysiological correlates of mental processes (Sur and Sinha 2009) . ERPs generated in later parts reflect the manner in which the subject evaluates the stimulus and are termed ‘cognitive’ or ‘endogenous’ ERPs as they examine information processing. The waveforms are described according to latency and amplitude.
In our study we will focus on measuring sensory gating and cognitive functions using P50 and P300 waveforms before and after the rTMS treatment.
P50 is a component as the most positive peak between 30 and 70 ms post-stimulus (auditory) onset. In a double auditory stimulus paradigm, the P50 response amplitude of the second (S2) or test stimulus [to that of the first (S1) or conditioned stimulus] demonstrates sensory gating. Deficits in sensory gating are an important endophenotype for schizophrenia (Toyomaki et al. 2015). P50 ratio between S1 and S2 amplitudes will therefore be calculated to measure sensory gating.
EEG recording and analysis - based on (Toyomaki et al. 2015):
Electroencephalogram (EEG: bandpass 0.16–30 Hz, digitized at 500 Hz) recording was obtained from Fz, Cz, and Pz electrodes according to the international 10/20 system. Ag/AgCl electrodes were used, and impedance was kept below 10 kΩ. All electrodes were referenced to the earlobes. Electro-oculogram (EOG) recording was gathered from electrodes lateral to and below the left eye. The paired-click paradigm was performed to elicit the P50 component. A pure tone (1500 Hz, 6-ms duration, 80 dB SPL) was used as the click sound and presented during a 500-ms interval through a loudspeaker.
The interval between paired stimuli was 8 seconds. The signals were digitized for an epoch of 400 ms starting 200 ms prior to the presentation of each auditory stimulus. Individual trials were rejected when EEG voltage was greater than ±35 μV, indicative of excessive muscle activity, eye movements, or other artifacts. We defined the P50 component as the most positive peak between 30 and 70 ms post-stimulus onset. We measured the peak-to-peak P50 amplitude from a preceding negative trough to the positive peak. This was done because the baseline prior to the second stimulus onset often fluctuated based on the ERP from the first stimulus; the baseline-to-peak P50 amplitude was not appropriate for assessment. The P50 ratio was calculated as the test stimulus response divided by the conditioning stimulus response. We presented the paired stimulus 300 times, which provided 40 minutes of EEG measurement. In consideration of participant load and ear comfort that could influence EEG measurement, we instructed participants to watch a silent film and presented auditory stimuli from a loudspeaker as mentioned above.
Method - based on (Olincy and Martin 2005) :
Recordings will be obtained after the EEG recording with the same settings. Subjects will be in a supine position and staring at a fixed target to maintain alertness. Recordings will be obtained from subjects at least 30 minutes after their last cigarette, since nicotine has been shown to enhance P50 suppression in subjects with schizophrenia . Electroencephalogram (EEG) activity will be amplified 20,000 times with bandpass filters (–50%) between 1 and 300 Hz. Electrodes at the right superior orbit and lateral canthus recorded electrooculogram (EOG) activity. EEG and EOG data will be recorded for 1000 msec for each paired stimulus presented. The operator rejected trials during online recording if they contained large muscle artifact or eye blinks, as indicated by an EEG or EOG voltage of ±50 μV over the area of the P50 wave.
A conditioning-testing paradigm will present 2 similar auditory stimuli with an intrapair interval of 0.5 seconds and interstimulus interval of 10 seconds. A 0.04-msec duration square wave pulse will be amplified in the 20–12,000 Hz bandwidth and delivered through earphones that produced a 2.5-msec sound with a mean intensity of a 70-db sound pressure level, as measured at the subject’s ear by a sound meter. At least five average evoked potential recordings will be collected for each subject, each containing at least 16 trials. A high-pass filter (10 Hz) and a seven point, low-pass filter (300 Hz; A=0.95) digitally filtered each recording. The grand average used for analysis will exclude averaged recordings with no discernible conditioning P50 waves or with prominent EOG activity at the same latency as the P50 (Olincy and Martin 2005).
Supplementary data for the method (Fresán et al. 2007) :
Sensory gating evaluated by recording the P50 wave of the auditory evoked response in a paired-stimulus or conditioning-testing paradigm, (S1, conditioning click; S2, testing click; 500 ms interclick interval; 10,000 ms inter-pair interval). Five runs, each consisting of 30 identical pairs of clicks (150 total trials), were recorded. EEG register will be done according to International 10–20 System, using ANT Neuro waveguard EEG cap. Electrode resistances will be set less than 10 kΩ. The recording from scalp sites FP1, FP2, F7, F3, Fz, F4, F8, T7, C3, Cz, C4, T8, P7, P3, Pz, P4, P8 and Oz referenced to the average of left and right mastoid electrodes. Data will be collected at a sampling rate of 2000 Hz with an online analog band-pass filter of .05–500 Hz. Data epochs from −100 ms to 200 ms will be extracted and analyzed.
P300 responses to novel auditory stimuli might be used for investigating aspects of prefrontal function suspected of playing a substantial role in schizophrenic pathophysiology (Merrin et al. 2006). The P300 response has been shown to be reduced in schizophrenics, especially in the auditory system. P300 is a ERP that is elicited when people are paying attention to a task specific stimulus. It is thought to be connected to updating information in working memory. In our study P300 response will be measured with EEG where patients will be presented with an auditory oddball paradigm attention task.
Method - based on (Stefánsson and Jónsdóttir 1996):
The recordings will be carried out between 9 and 12 AM. The subjects will be lying in a comfortably chair with their eyes closed. The auditory stimuli, will be presented binaurally through headphones at an intensity level of 75 dB, consisted of a series of 250-Hz non-target tones and 1000-Hz target tones. The interstimulus interval between tones will be constant at 1.1 sec; tone duration 20 msec and rise/fall time will be 2.5 msec. For each subject there were two or three trials with at least 200 tones presented in each trial. The subjects will be asked to count the 1000-Hz tones, which will occur randomly with a probability of 0.2. At the end of each trial the subjects will be asked how many tones they had counted. The ERP signals will be recorded from 256 and 64 scalp electrodes , using ANT Neuro EEG system.
In the method used by Stefánsson and Jónsdóttir in 1996 in Icelandic patients with schizophrenia, the signals were filtered with a band-pass filter (0.1-100 Hz, -3dB) and digitized with a sampling rate of 500 Hz. The ERPs elicited by the 250-Hz and 1000-Hz tones were obtained by on-line computer averaging of the responses elicited by each type of stimulus. Each ERP signal had a duration of 510 msec, beginning immediately after stimulus presentation. Automatic eye movement artifact rejection was used, based on signal amplitude (>50 ~V or < -50 ~V) in frontal channels (F7, F3, Fz, F4, F8).
CSP will be induced with TMS and measured with electromyography (EMG). Patients will be instructed to maintain muscle contraction while a single suprathreshold TMS pulse is applied to the motor cortex contralaterally. The motor evoked potential arrests muscle activity for a certain amount of time which will be measured (McClintock, Freitas, Oberman, Lisanby, & Pascual-Leone, 2011). Cutaneous silent period (CuSP) will be used to calculate the CSP/CuSP ratio which will be used as a more robust parametter to assess the central inhibitory mechanisms before and after the treatment.
Resting motor threshold will be measured before each rTMS session to define treatment intensity. EMG will be used to measure MEP by using the right hand abductor pollicis brevis muscle 50-100 µV peak-to-peak. RMT will be defined as the intensity required to evoke MEP twitch in 5 out of 10 stimuli (Möller, Hjaltason, Ívarsson, & Stefánsson, 2006).
References:
Baradits, M., S. Bálint, B. Kakuszi, I. Bitter, and P. Czobor. 2016. “Gamma Band Activity in Spontaneous EEG in Patients with Schizophrenia.” European Neuropsychopharmacology: The Journal of the European College of Neuropsychopharmacology 26: S344–45.
Fresán, Ana, Rogelio Apiquian, María García-Anaya, Camilo de la Fuente-Sandoval, Humberto Nicolini, and Ariel Graff-Guerrero. 2007. “The P50 Auditory Evoked Potential in Violent and Non-Violent Patients with Schizophrenia.” Schizophrenia Research 97 (1-3): 128–36.
Kropotov, Juri D. 2010. Quantitative EEG, Event-Related Potentials and Neurotherapy. Academic Press.
Merrin, Edward L., Thomas C. Floyd, Raymond F. Deicken, and Patricia A. Lane. 2006. “The Wisconsin Card Sort Test and P300 Responses to Novel Auditory Stimuli in Schizophrenic Patients.” International Journal of Psychophysiology: Official Journal of the International Organization of Psychophysiology 60 (3): 330–48.
Mitra, Sayantanava, S. Haque Nizamie, Nishant Goyal, and Sai Krishna Tikka. 2015. “Evaluation of Resting State Gamma Power as a Response Marker in Schizophrenia.” Psychiatry and Clinical Neurosciences 69 (10): 630–39.
Nuwer, M. 1997. “Assessment of Digital EEG, Quantitative EEG, and EEG Brain Mapping: Report of the American Academy of Neurology and the American Clinical Neurophysiology Society.” Neurology 49 (1): 277–92.
Olincy, Ann, and Laura Martin. 2005. “Diminished Suppression of the P50 Auditory Evoked Potential in Bipolar Disorder Subjects With a History of Psychosis.” The American Journal of Psychiatry 162 (1): 43–49.
Stefánsson, S. B., and T. J. Jónsdóttir. 1996. “Auditory Event-Related Potentials, Auditory Digit Span, and Clinical Symptoms in Chronic Schizophrenic Men on Neuroleptic Medication.” Biological Psychiatry 40 (1): 19–27.
Sur, Shravani, and V. K. Sinha. 2009. “Event-Related Potential: An Overview.” Industrial Psychiatry Journal 18 (1): 70.
Toyomaki, Atsuhito, Naoki Hashimoto, Yuki Kako, Yoshiro Tomimatsu, Tsukasa Koyama, and Ichiro Kusumi. 2015. “Different P50 Sensory Gating Measures Reflect Different Cognitive Dysfunctions in Schizophrenia.” Schizophrenia Research. Cognition 2 (3): 166–69.
Williams, Sylvain. 2010. “Gamma Oscillations and Schizophrenia.” Journal of Psychiatry & Neuroscience: JPN 35 (2): 75–77.