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Research paper thumbnail of Steady-State Visually Evoked Potential Topography during Processing of Emotional Valence in Healthy Subjects

NeuroImage, Dec 1, 2002

The International Affective Picture System (IAPS) is increasingly used in brain imaging studies t... more The International Affective Picture System (IAPS) is increasingly used in brain imaging studies to examine emotional processes. This task allows valence and arousal content to be systematically investigated; however, previous studies have generally failed to select images that vary in one dimension as well as hold constant the variability on the other dimension. In addition, no studies have investigated the temporal structure associated with the conscious, ongoing processing of emotional stimuli following systematic selection of IAPS images. The aim of the present study was therefore to use steady-state probe topography (SSPT) to examine the steady-state visually evoked potentials (SSVEPs) associated with the processing of pleasant and unpleasant images low in arousal content. Seventy-five IAPS images, categorized as unpleasant, neutral, or pleasant, were presented to 16 healthy subjects while brain activity was recorded from 64 scalp sites. Analysis subtracted the activity associated with the presentation of neutral images from the activity associated with the presentation of pleasant as well as unpleasant images. Results demonstrate that both pleasant and unpleasant valence is associated with transient, widespread, and bilateral frontal SSVEP latency reductions. Unpleasant images were also associated with a transient bilateral anterior frontal amplitude decrease. Latency reductions are interpreted as increases in neural information processing speed, while amplitude reductions are interpreted in the current paper as analogous to an event-related desynchronisation commonly associated with the alpha bandwidth. These key findings support previous literature in terms of there being substantial overlap in frontal neural circuitry when the brain processes pleasant and unpleasant valence relative to neutral valence.

Research paper thumbnail of Research at the National Bureau of Standards applicable to long-distance location and direction-finding problems

Journal of Research of the National Bureau of Standards, Section D: Radio Propagation, 1961

~ .R esearch pertainin g to radio-location and direction-finding prob lems conducted aL Lhe I\atl... more ~ .R esearch pertainin g to radio-location and direction-finding prob lems conducted aL Lhe I\atlOnal Bureau of Standards sin ce 1941 includes evolution of a tec hnique for determining polariz at ion error, study of non-great-circle bearings, t he de velopmenL of a rapidscannin g directional ante n na, a nd t he development of Loran-C wit h its prec is ion Liming capabilities .

Research paper thumbnail of The steady state visually evoked potential and topography and vigilance

We report data which demonstrates a correlation between the magnitude of the Steady State Visuall... more We report data which demonstrates a correlation between the magnitude of the Steady State Visually Evoked Potential (SSVEP) and visual vigilance. The SSVEP was recorded from 64 scalp sites and elicited by a 13 Hz uniform visual flicker presented while subjects undertook a visual vigilance task. Fifteen right-handed males were required to view three times a 180 second series of geometrical shapes; a continuous sequence of 60 squares, 60 circles and finally 60 squares. Just prior to the final trial subjects were asked to identify a target circle. A comparison of the last two trials indicated that the appearance of the target circle was associated with a transient SSVEP attenuation in the occipito-parietal and right pre-frontal regions. The same comparison indicated a pronounced SSVEP attenuation in the centro-parietal region peaking after the appearance of the circles. The distribution of the attenuation at the pre-frontal, centro-parietal and occipito-parietal regions was lateralised with the right hemisphere showing pronounced and long lasting effects. Aspects of normal brain function and dysfunction can be further explored using this novel technique.

Research paper thumbnail of Artifact sensitivity of Fourier-based analysis of steady-state visually evoked potential

Biological Psychology, 1993

Research paper thumbnail of Steady-state probe topography in a recognition memory task

Biological Psychology, 1993

Research paper thumbnail of Effects of stimulants on brain electrical activity in subtypes of attention deficit hyperactivity disorder

Research paper thumbnail of Working memory and intelligence: Why do smarter people remember more?

Research paper thumbnail of Dynamic changes in brain evoked potentially laterality in a visual vigilance task

Research paper thumbnail of The stop-signal task: a comparison of auditory and visual stop-signals set proportional to mean reaction time

Research paper thumbnail of Individual differences in steady state visually evoked potential synchronization during mental rotation

International Journal of Psychophysiology, 2002

Research paper thumbnail of Effects of flavonoids on brain functional connectivity

Research paper thumbnail of Dynamic Sculpting of Brain Functional Connectivity Is Correlated with Performance

Brain Topography, 2003

In this study, we examined the relationship between cortical coupling, reflected in event related... more In this study, we examined the relationship between cortical coupling, reflected in event related partial coherence (ERPC) and cognitive processing speed while subjects performed a set of Raven's Progressive Matrices (RPM), a task used to measure IQ. Fifty-five participants (29 males) performed a computerized version of the RPM where they were required to identify the shape (probe) that is consistent with a matrix of displayed shapes. Participants indicated a match or non-match by pressing a micro-switch with either the right or left hand. The steady state visually evoked potential (SSVEP) was elicited by a 13 Hz uniform visual flicker superimposed over the visual fields and the SSVEP event-related coherence (SSVEP-ERPC) calculated for all 2016 unique electrode pairs. The linear correlation between SSVEP-ERPC and processing speed (the inverse of reaction time) was calculated for all electrode pairs for all time points during the 3 sec interval that the probes were on the screen. Using correlation coefficient thresholds corresponding to p=0.001 we identified those electrode pairs where SSVEP-ERPC or neural synchronization was significantly correlated with processing speed. At a point 0.8 sec before the appearance of the probe we observed that the synchronization between specific prefrontal, frontal and central sites was correlated with processing speed. We suggest that this relationship may reflect the efficiency of working memory processes and speed of information processing.

Research paper thumbnail of On the relationship of synaptic activity to macroscopic measurements: does co-registration of EEG with fMRI make sense?

A two-scale theoretical description outlines relationships between brain current sources and the ... more A two-scale theoretical description outlines relationships between brain current sources and the resulting extracranial electric field, recorded as EEG. Finding unknown sources of EEG, the so-called "inverse problem", is discussed in general terms, with emphasis on the fundamental non-uniqueness of inverse solutions. Hemodynamic signatures, measured with fMRI, are expressed as voxel integrals to facilitate comparisons with EEG. Two generally distinct cell groups (1 and 2), generating EEG and fMRI signals respectively, are embedded within the much broader class of synaptic action fields. Cell groups 1 and 2 may or may not overlap in specific experiments. Implications of this incomplete overlap for co-registration studies are considered. Each experimental measure of brain function is generally sensitive to a different kind of source activity and to different spatial and temporal scales. Failure to appreciate such distinctions can exacerbate conflicting views of brain functio...

Research paper thumbnail of Electrophysiological correlates of static and dynamic facial emotions

Research paper thumbnail of Neurophysiology and psychopharmacology of anticipatory anxiety

Research paper thumbnail of Test-retest reliability of steady state visually evoked potentials (SSVEP) during presentation of affective cognitive tasks: the emotional stroop (ES) and the international affective picture system (IAPS)

Research paper thumbnail of The Steady State Visual Evoked Response and Estimates of Phase Velocity

Biomag 96

Several models of brain function predict the existence of wave like phenomena where electrical ac... more Several models of brain function predict the existence of wave like phenomena where electrical activity travels from one cortical region to another [1–3]. A model which can explain the rhythmogenesis of the MEG and EEG should approximate neural mass dynamics at a spatial scale consistent with that of scalp recordings. In this respect, Nunez’s global resonance model is of particular relevance since it allows direct comparison between scalp recorded electrical activity and theory [3]. This model predicts waves mediated by the rapidly conducting cortico-cortical fibres with speeds between 6 to 9 m/sec. Hence, a specific test of the model can be made by measuring the velocity of MEG and EEG signals and comparing estimated values with the above range. A direct approach is to use the Steady State Visual Evoked Response (SSVER) and measure the spatial change in phase across the scalp. In this paper the SSVER phase is measured at regular intervals on the scalp and the resulting phase topography yields an estimate of phase velocity at the stimulus frequency. In addition, estimates of wavenumber are obtained from the same measurement.

Research paper thumbnail of Acetylcholine and normal variations in intelligence

Research paper thumbnail of Steady state visually evoked potential topography of unfamiliar facial processing

To examine the latency topography of the steady-state visually evoked potential (SSVEP) in patien... more To examine the latency topography of the steady-state visually evoked potential (SSVEP) in patients diagnosed with schizophrenia and normal controls while undertaking a visual vigilance task. Twenty patients diagnosed with schizophrenia and 18 normal controls performed the A-X version of the continuous performance task (CPT A-X) where subjects are required to press a micro-switch on the unpredictable appearance of an 'X' that had been preceded by an 'A.' Brain electrical activity was recorded from 64 scalp sites and a 13 Hz spatially uniform visual flicker presented with the task was used to elicit a steady-state visually evoked potential (SSVEP). Following the appearance of the 'A' and 'X,' the control group demonstrated a transient SSVEP latency reduction at parietal and prefrontal sites. By contrast, the patients group showed no such SSVEP latency reduction. The prefrontal SSVEP latency changes in the 500 ms interval following the appearance of the 'X' were correlated with mean individual reaction time in both populations. We suggest that the SSVEP latency reduction may index excitatory processes and that the absence of prefrontal SSVEP latency reduction in schizophrenic patients may be a manifestation of reduced prefrontal activity or 'hypofrontality' observed with other neuroimaging modalities.

Research paper thumbnail of Prefrontal and Parietal Deficits in ADHD Suggested by Brain Electrical Activity Mapping During Children's Performance of the AX CPT

The Australian Educational and Developmental Psychologist, 1996

Nine children meeting DSM-III-R criteria for Attention Deficit Hyperactivity Disorder (ADHD) and ... more Nine children meeting DSM-III-R criteria for Attention Deficit Hyperactivity Disorder (ADHD) and eighteen normal children participated in this study. A screening assessment revealed significantly more behavioural and academic problems in the ADHD group. Subjects performed a low demand visual vigilance task (the reference task) and the AX version of the continuous perfonnance task (CPT), while the steady-state visually evoked potential (SSVEP) was continuously recorded from 64 scalp electrode sites. The topography of the SSVEP amplitude difference between the reference and AX tasks was examined. In the 3.5 second interval between the appearances of the “A” and the “X” normal children showed transient reductions in right prefrontal SSVEP amplitude and a sustained reduction in right parieto-occipital SSVEP amplitude. These reductions in SSVEP amplitude were not seen in ADHD subjects. These results suggest that the presentation of a priming stimulus is associated with increased activati...

Research paper thumbnail of Steady-State Visually Evoked Potential Topography during Processing of Emotional Valence in Healthy Subjects

NeuroImage, Dec 1, 2002

The International Affective Picture System (IAPS) is increasingly used in brain imaging studies t... more The International Affective Picture System (IAPS) is increasingly used in brain imaging studies to examine emotional processes. This task allows valence and arousal content to be systematically investigated; however, previous studies have generally failed to select images that vary in one dimension as well as hold constant the variability on the other dimension. In addition, no studies have investigated the temporal structure associated with the conscious, ongoing processing of emotional stimuli following systematic selection of IAPS images. The aim of the present study was therefore to use steady-state probe topography (SSPT) to examine the steady-state visually evoked potentials (SSVEPs) associated with the processing of pleasant and unpleasant images low in arousal content. Seventy-five IAPS images, categorized as unpleasant, neutral, or pleasant, were presented to 16 healthy subjects while brain activity was recorded from 64 scalp sites. Analysis subtracted the activity associated with the presentation of neutral images from the activity associated with the presentation of pleasant as well as unpleasant images. Results demonstrate that both pleasant and unpleasant valence is associated with transient, widespread, and bilateral frontal SSVEP latency reductions. Unpleasant images were also associated with a transient bilateral anterior frontal amplitude decrease. Latency reductions are interpreted as increases in neural information processing speed, while amplitude reductions are interpreted in the current paper as analogous to an event-related desynchronisation commonly associated with the alpha bandwidth. These key findings support previous literature in terms of there being substantial overlap in frontal neural circuitry when the brain processes pleasant and unpleasant valence relative to neutral valence.

Research paper thumbnail of Research at the National Bureau of Standards applicable to long-distance location and direction-finding problems

Journal of Research of the National Bureau of Standards, Section D: Radio Propagation, 1961

~ .R esearch pertainin g to radio-location and direction-finding prob lems conducted aL Lhe I\atl... more ~ .R esearch pertainin g to radio-location and direction-finding prob lems conducted aL Lhe I\atlOnal Bureau of Standards sin ce 1941 includes evolution of a tec hnique for determining polariz at ion error, study of non-great-circle bearings, t he de velopmenL of a rapidscannin g directional ante n na, a nd t he development of Loran-C wit h its prec is ion Liming capabilities .

Research paper thumbnail of The steady state visually evoked potential and topography and vigilance

We report data which demonstrates a correlation between the magnitude of the Steady State Visuall... more We report data which demonstrates a correlation between the magnitude of the Steady State Visually Evoked Potential (SSVEP) and visual vigilance. The SSVEP was recorded from 64 scalp sites and elicited by a 13 Hz uniform visual flicker presented while subjects undertook a visual vigilance task. Fifteen right-handed males were required to view three times a 180 second series of geometrical shapes; a continuous sequence of 60 squares, 60 circles and finally 60 squares. Just prior to the final trial subjects were asked to identify a target circle. A comparison of the last two trials indicated that the appearance of the target circle was associated with a transient SSVEP attenuation in the occipito-parietal and right pre-frontal regions. The same comparison indicated a pronounced SSVEP attenuation in the centro-parietal region peaking after the appearance of the circles. The distribution of the attenuation at the pre-frontal, centro-parietal and occipito-parietal regions was lateralised with the right hemisphere showing pronounced and long lasting effects. Aspects of normal brain function and dysfunction can be further explored using this novel technique.

Research paper thumbnail of Artifact sensitivity of Fourier-based analysis of steady-state visually evoked potential

Biological Psychology, 1993

Research paper thumbnail of Steady-state probe topography in a recognition memory task

Biological Psychology, 1993

Research paper thumbnail of Effects of stimulants on brain electrical activity in subtypes of attention deficit hyperactivity disorder

Research paper thumbnail of Working memory and intelligence: Why do smarter people remember more?

Research paper thumbnail of Dynamic changes in brain evoked potentially laterality in a visual vigilance task

Research paper thumbnail of The stop-signal task: a comparison of auditory and visual stop-signals set proportional to mean reaction time

Research paper thumbnail of Individual differences in steady state visually evoked potential synchronization during mental rotation

International Journal of Psychophysiology, 2002

Research paper thumbnail of Effects of flavonoids on brain functional connectivity

Research paper thumbnail of Dynamic Sculpting of Brain Functional Connectivity Is Correlated with Performance

Brain Topography, 2003

In this study, we examined the relationship between cortical coupling, reflected in event related... more In this study, we examined the relationship between cortical coupling, reflected in event related partial coherence (ERPC) and cognitive processing speed while subjects performed a set of Raven's Progressive Matrices (RPM), a task used to measure IQ. Fifty-five participants (29 males) performed a computerized version of the RPM where they were required to identify the shape (probe) that is consistent with a matrix of displayed shapes. Participants indicated a match or non-match by pressing a micro-switch with either the right or left hand. The steady state visually evoked potential (SSVEP) was elicited by a 13 Hz uniform visual flicker superimposed over the visual fields and the SSVEP event-related coherence (SSVEP-ERPC) calculated for all 2016 unique electrode pairs. The linear correlation between SSVEP-ERPC and processing speed (the inverse of reaction time) was calculated for all electrode pairs for all time points during the 3 sec interval that the probes were on the screen. Using correlation coefficient thresholds corresponding to p=0.001 we identified those electrode pairs where SSVEP-ERPC or neural synchronization was significantly correlated with processing speed. At a point 0.8 sec before the appearance of the probe we observed that the synchronization between specific prefrontal, frontal and central sites was correlated with processing speed. We suggest that this relationship may reflect the efficiency of working memory processes and speed of information processing.

Research paper thumbnail of On the relationship of synaptic activity to macroscopic measurements: does co-registration of EEG with fMRI make sense?

A two-scale theoretical description outlines relationships between brain current sources and the ... more A two-scale theoretical description outlines relationships between brain current sources and the resulting extracranial electric field, recorded as EEG. Finding unknown sources of EEG, the so-called "inverse problem", is discussed in general terms, with emphasis on the fundamental non-uniqueness of inverse solutions. Hemodynamic signatures, measured with fMRI, are expressed as voxel integrals to facilitate comparisons with EEG. Two generally distinct cell groups (1 and 2), generating EEG and fMRI signals respectively, are embedded within the much broader class of synaptic action fields. Cell groups 1 and 2 may or may not overlap in specific experiments. Implications of this incomplete overlap for co-registration studies are considered. Each experimental measure of brain function is generally sensitive to a different kind of source activity and to different spatial and temporal scales. Failure to appreciate such distinctions can exacerbate conflicting views of brain functio...

Research paper thumbnail of Electrophysiological correlates of static and dynamic facial emotions

Research paper thumbnail of Neurophysiology and psychopharmacology of anticipatory anxiety

Research paper thumbnail of Test-retest reliability of steady state visually evoked potentials (SSVEP) during presentation of affective cognitive tasks: the emotional stroop (ES) and the international affective picture system (IAPS)

Research paper thumbnail of The Steady State Visual Evoked Response and Estimates of Phase Velocity

Biomag 96

Several models of brain function predict the existence of wave like phenomena where electrical ac... more Several models of brain function predict the existence of wave like phenomena where electrical activity travels from one cortical region to another [1–3]. A model which can explain the rhythmogenesis of the MEG and EEG should approximate neural mass dynamics at a spatial scale consistent with that of scalp recordings. In this respect, Nunez’s global resonance model is of particular relevance since it allows direct comparison between scalp recorded electrical activity and theory [3]. This model predicts waves mediated by the rapidly conducting cortico-cortical fibres with speeds between 6 to 9 m/sec. Hence, a specific test of the model can be made by measuring the velocity of MEG and EEG signals and comparing estimated values with the above range. A direct approach is to use the Steady State Visual Evoked Response (SSVER) and measure the spatial change in phase across the scalp. In this paper the SSVER phase is measured at regular intervals on the scalp and the resulting phase topography yields an estimate of phase velocity at the stimulus frequency. In addition, estimates of wavenumber are obtained from the same measurement.

Research paper thumbnail of Acetylcholine and normal variations in intelligence

Research paper thumbnail of Steady state visually evoked potential topography of unfamiliar facial processing

To examine the latency topography of the steady-state visually evoked potential (SSVEP) in patien... more To examine the latency topography of the steady-state visually evoked potential (SSVEP) in patients diagnosed with schizophrenia and normal controls while undertaking a visual vigilance task. Twenty patients diagnosed with schizophrenia and 18 normal controls performed the A-X version of the continuous performance task (CPT A-X) where subjects are required to press a micro-switch on the unpredictable appearance of an 'X' that had been preceded by an 'A.' Brain electrical activity was recorded from 64 scalp sites and a 13 Hz spatially uniform visual flicker presented with the task was used to elicit a steady-state visually evoked potential (SSVEP). Following the appearance of the 'A' and 'X,' the control group demonstrated a transient SSVEP latency reduction at parietal and prefrontal sites. By contrast, the patients group showed no such SSVEP latency reduction. The prefrontal SSVEP latency changes in the 500 ms interval following the appearance of the 'X' were correlated with mean individual reaction time in both populations. We suggest that the SSVEP latency reduction may index excitatory processes and that the absence of prefrontal SSVEP latency reduction in schizophrenic patients may be a manifestation of reduced prefrontal activity or 'hypofrontality' observed with other neuroimaging modalities.

Research paper thumbnail of Prefrontal and Parietal Deficits in ADHD Suggested by Brain Electrical Activity Mapping During Children's Performance of the AX CPT

The Australian Educational and Developmental Psychologist, 1996

Nine children meeting DSM-III-R criteria for Attention Deficit Hyperactivity Disorder (ADHD) and ... more Nine children meeting DSM-III-R criteria for Attention Deficit Hyperactivity Disorder (ADHD) and eighteen normal children participated in this study. A screening assessment revealed significantly more behavioural and academic problems in the ADHD group. Subjects performed a low demand visual vigilance task (the reference task) and the AX version of the continuous perfonnance task (CPT), while the steady-state visually evoked potential (SSVEP) was continuously recorded from 64 scalp electrode sites. The topography of the SSVEP amplitude difference between the reference and AX tasks was examined. In the 3.5 second interval between the appearances of the “A” and the “X” normal children showed transient reductions in right prefrontal SSVEP amplitude and a sustained reduction in right parieto-occipital SSVEP amplitude. These reductions in SSVEP amplitude were not seen in ADHD subjects. These results suggest that the presentation of a priming stimulus is associated with increased activati...