Dynamics of event-related potentials to trains of light and dark flashes: responses to missing and extra stimuli in elasmobranch fish.

To characterize the dependencies of ERPs in lower vertebrates and brain levels upon recent history and sequences of stimuli, trains of flashes were delivered at various frequencies to unanesthetized rays while recording in optic tectum and telencephalon. ERPs to repetitive stimuli cannot be understood in terms of simple refractoriness and recovery. Processes must be invoked such as simultaneous excitation and suppression, facilitation and its opposite, rebound and induced rhythms, each with development and decay times and nonlinearities. Some of these processes are uncovered by omitting a stimulus from a train. Omitted stimulus potentials (OSPs) act as though the brain expects a stimulus within 5-7 ms of the interstimulus interval (ISI) of the train. Very few ISIs suffice. The effect upon VEP form and duration of the number of stimuli in short trains, before the steady state response (SSR) is established, is complex. Alternation of the amplitude of successive VEPs (1 large every 2 VEPs, 1 in 3, 1 in 4) is one indication of complexities in the SSR. OSPs also alternate. A single extra stimulus interpolated into a regular train causes distinct effects according to its position. Sharp discontinuities in these effects appear with <5 ms shifts. Total power of the SSR decreases with stimulation frequency but there is a large peak of increased power at 7 Hz and another at 12 Hz. Induced rhythms are a labile, late phase of OSPs as well as of rested VEPs and of the OFF response to a long light pulse. Jittered ISI experiments show that the apparent expectation of the OSP is little affected and that the intervals in the last few hundred milliseconds are most influential. The OSP studied here (ISI <0.5 s)is quite different from that so far studied in human subjects (ISI >1s). We predict further similarities when each taxon is tested in the other ISI range. A major category of response characteristics, besides sensitivity, receptive fields and recovery times, is dependence upon recent history of iterative events, including intervals, delays, omissions and perhaps multiple facilitating and forgetting time constants. The variables examined parametrically in this study are only some of those available. Such dynamical characteristics are important neglected properties of afferent systems at each level

The effects of interstimulus interval on sensory gating and on preattentive auditory memory in the oddball paradigm. Can magnitude of the sensory gating affect preattentive auditory comparison process?

İstanbul Bilim Üniversitesi, Tıp Fakültesi.P50, and mismatch negativity (MMN) are components of event-related potentials (ERP) reflecting sensory gating and preattentive auditory memory, respectively. Interstimulus interval (ISI) is an important determinant of the amplitudes of these components and N1. In the present study the interrelation between stimulus gating and preattentive auditory sensory memory were investigated as a function of ISI in 1.5, 2.5 and 3.5 s in 15 healthy volunteered participants. ISI factor affected the N1 peak amplitude significantly. MMN amplitude in 2.5 s ISI was significantly smaller compared to 1.5 and 3.5 s ISI. ISI X stimuli interaction on P50 amplitude was statistically significant. P50 amplitudes to deviant stimuli in 2.5 s ISI were larger than the P50 amplitudes in other ISIs. P50 difference (P50d) waveform amplitude correlated significantly with MMN amplitude. The results suggest that: (i) auditory sensory gating could affect preattentive auditory sensory memory by supplying input to the comparator mechanism; (ii) 2.5 s ISI is important in displaying the sensory gating and preattentive auditory sensory memory relation

Event-related potentials during auditory oddball, and combined auditory oddball-visual paradigms.

İstanbul Bilim Üniversitesi, Tıp Fakültesi.The purpose of the current study was to investigate the properties of a new modification of the classical auditory oddball paradigm (auditory oddballparadigm combined with passive visual stimulation, AERPs + VEPs) and compare the scalp topography obtained with the new paradigm and the classical auditory oddball paradigm (AERPs) in healthy humans. The responses to bimodal stimulation, and to the classical oddball paradigm were similar to those reported in other studies in terms of location, amplitudes, and latencies of P1, N1, P2, N2, and P300. The new modification of theoddball paradigm produced P300 at fronto-central locations in contrast to centro-parietal locations during the classical oddball paradigm. The amplitudes and latencies of P300 were also significantly larger during the new than the classical paradigm. Furthermore, the amplitudes of N1 and P2, but not N2 were significantly higher and differed in location during the new paradigm in response to both target and standard stimuli. The latencies of all three waves were significantly longer and the latency of P2 differed in location between the new and the classical paradigms in response to only the standard stimuli. The results of this study suggest that the new modification of the classical oddball paradigm produces different neural responses to the classical oddball paradigm. Therefore, this modification can be used to investigate dysfunctions in sensory and cognitive processing in clinical samples

Event related potentials to mental arithmetic during cold stress

İstanbul Bilim Üniversitesi, Tıp Fakültesi.AMAÇ: Tek başına ve soğuk stres (SS) sırasında Zihinsel aritmetik hesaplamanın (ZA) Go/NoGo paradigması kullanılarak olaya ilişkin beyin potansiyelleri bağlamında incelenmesi. GEREÇ ve YÖNTEM: Gönüllü üniversite öğrencisi 7 deneğin 11 kanaldan EEG kaydı yapıldı. Deneklerin işlem yapmadıkları, soğuk stres altında oldukları, aritmetik işlem yaptıkları ve soğuk stres sırasında aritmetik işlem yaptıkları durumlarda kan basınçları ve kalp atımları ölçüldü. EEG kayıtlar ZA ve ZA +SS koşullarında Go/NoGO paradigması sırasında alındı. Deneklere ekranda 400 ms süre ile aritmetik bir işlem ve bundan 700 ms sonra sonuç gösterildi. Deneklerden, gösterilen sonuç doğru ise düğmeye basmaları yanlış ise basmamaları istendi