Emi Tanaka

A transition from unimodal to multimodal activations in four sensory modalities in humans: an electrophysiological study

BackgroundTo investigate the long-latency activities common to all sensory modalities, electroencephalographic responses to auditory (1000 Hz pure tone), tactile (electrical stimulation to the index finger), visual (simple figure of a star), and noxious (intra-epidermal electrical stimulation to the dorsum of the hand) stimuli were recorded from 27 scalp electrodes in 14 healthy volunteers.ResultsResults of source modeling showed multimodal activations in the anterior part of the cingulate cortex (ACC) and hippocampal region (Hip). The activity in the ACC was biphasic. In all sensory modalities, the first component of ACC activity peaked 30–56 ms later than the peak of the major modality-specific activity, the second component of ACC activity peaked 117–145 ms later than the peak of the first component, and the activity in Hip peaked 43–77 ms later than the second component of ACC activity.ConclusionThe temporal sequence of activations through modality-specific and multimodal pathways was similar among all sensory modalities.

Change-driven cortical activation in multisensory environments: An MEG study

The quick detection of dynamic changes in multisensory environments is essential to survive dangerous events and orient attention to informative events. Previous studies have identified multimodal cortical areas activated by changes of visual, auditory, and tactile stimuli. In the present study, we used magnetoencephalography (MEG) to examine time-varying cortical processes responsive to unexpected unimodal changes during continuous multisensory stimulation. The results showed that there were change-driven cortical responses in multimodal areas, such as the temporo-parietal junction and middle and inferior frontal gyri, regardless of the sensory modalities where the change occurred. These multimodal activations accompanied unimodal activations, both of which in general had some peaks within 300 ms after the changes. Thus, neural processes responsive to unimodal changes in the multisensory environment are distributed at different timing in these cortical areas.

Multi-Dimensional Dynamics of Human Electromagnetic Brain Activity

Magnetoencephalography (MEG) and electroencephalography (EEG) are invaluable neuroscientific tools for unveiling human neural dynamics in three dimensions (space, time, and frequency), which are associated with a wide variety of perceptions, cognition, and actions. MEG/EEG also provides different categories of neuronal indices including activity magnitude, connectivity, and network properties along the three dimensions. In the last 20 years, interest has increased in inter-regional connectivity and complex network properties assessed by various sophisticated scientific analyses. We herein review the definition, computation, short history, and pros and cons of connectivity and complex network (graph-theory) analyses applied to MEG/EEG signals. We briefly describe recent developments in source reconstruction algorithms essential for source-space connectivity and network analyses. Furthermore, we discuss a relatively novel approach used in MEG/EEG studies to examine the complex dynamics represented by human brain activity. The correct and effective use of these neuronal metrics provides a new insight into the multi-dimensional dynamics of the neural representations of various functions in the complex human brain.

Cortical dynamics of visual change detection based on sensory memory

Detecting a visual change was suggested to relate closely to the visual sensory memory formed by visual stimuli before the occurrence of the change, because change detection involves identifying a difference between ongoing and preceding sensory conditions. Previous neuroimaging studies showed that an abrupt visual change activates the middle occipital gyrus (MOG). However, it still remains to be elucidated whether the MOG is related to visual change detection based on sensory memory. Here we tried to settle this issue using a new method of stimulation with blue and red LEDs to emphasize a memory-based change detection process. There were two stimuli, a standard trial stimulus and a deviant trial stimulus. The former was a red light lasting 500 ms, and the latter was a red light lasting 250 ms immediately followed by a blue light lasting 250 ms. Effects of the trial-trial interval, 250 approximately 2000 ms, were investigated to know how cortical responses to the abrupt change (from red to blue) were affected by preceding conditions. The brain response to the deviant trial stimulus was recorded by magnetoencephalography. Results of a multi-dipole analysis showed that the activity in the MOG, peaking at around 150 ms after the change onset, decreased in amplitude as the interval increased, but the earlier activity in BA 17/18 was not affected by the interval. These results suggested that the MOG is an important cortical area relating to the sensory memory-based visual change-detecting system.

Common cortical responses evoked by appearance, disappearance and change of the human face

BackgroundTo segregate luminance-related, face-related and non-specific components involved in spatio-temporal dynamics of cortical activations to a face stimulus, we recorded cortical responses to face appearance (Onset), disappearance (Offset), and change (Change) using magnetoencephalography.ResultsActivity in and around the primary visual cortex (V1/V2) showed luminance-dependent behavior. Any of the three events evoked activity in the middle occipital gyrus (MOG) at 150 ms and temporo-parietal junction (TPJ) at 250 ms after the onset of each event. Onset and Change activated the fusiform gyrus (FG), while Offset did not. This FG activation showed a triphasic waveform, consistent with results of intracranial recordings in humans.ConclusionAnalysis employed in this study successfully segregated four different elements involved in the spatio-temporal dynamics of cortical activations in response to a face stimulus. The results show the responses of MOG and TPJ to be associated with non-specific processes, such as the detection of abrupt changes or exogenous attention. Activity in FG corresponds to a face-specific response recorded by intracranial studies, and that in V1/V2 is related to a change in luminance.

Dynamics of within-, inter-, and cross-modal attentional modulation

Numerous studies have demonstrated effects of spatial attention within single sensory modalities (within-modal spatial attention) and the effect of directing attention to one sense compared with the other senses (intermodal attention) on cortical neuronal activity. Furthermore, recent studies have been revealing that the effects of spatial attention directed to a certain location in a certain sense spread to the other senses at the same location in space (cross-modal spatial attention). The present study used magnetoencephalography to examine the temporal dynamics of the effects of within-modal and cross-modal spatial and intermodal attention on cortical processes responsive to visual stimuli. Visual or tactile stimuli were randomly presented on the left or right side at a random interstimulus interval and subjects directed attention to the left or right when vision or touch was a task-relevant modality. Sensor-space analysis showed that a response around the occipitotemporal region at around 150 ms after visual stimulation was significantly enhanced by within-modal, cross-modal spatial, and intermodal attention. A later response over the right frontal region at around 200 ms was enhanced by within-modal spatial and intermodal attention, but not by cross-modal spatial attention. These effects were estimated to originate from the occipitotemporal and lateral frontal areas, respectively. Thus the results suggest different spatiotemporal dynamics of neural representations of cross-modal attention and intermodal or within-modal attention.

Neural representation of feature synergy

Interactive non-linear cooperation of different feature dimensions, feature synergy, has been studied in psychophysics, but the neural mechanism is unknown. The present study investigated the neural representation of feature synergy of two second-order visual features by combining electroencephalography (EEG) with the signal detection theory (SDT). Two kinds of a 27-by-27 array of Gabor patches were presented in a random order; a reference stimulus which has no segregated region, and a target stimulus whose inner region differed in spatial frequency, orientation, or both from the surround. Subjects performed a Yes-No discrimination of whether the inner region was different from the surround, while EEG signals were recorded from 62 locations. When the SDT measure showed feature synergy, EEG activity showed a long-lasting enhancement starting at 130 ms around the inferior temporal region. In contrast, no EEG modulation was observed when feature synergy was not present. Thus, our combined approach demonstrates that non-linear cooperation between different features is represented by neural activity starting at 130 ms post-stimulus in the ventral visual stream.

S142. Attentional gradient in touch: An MEG study

Introduction Previous studies have demonstrated the cortical mechanisms for the gradient of spatial attention in vision and audition, whereas those for touch have yet to be elucidated in detail. We used magnetoencephalography (MEG) to examine the within-hand gradient of tactile spatial attention in the cerebral cortex. Methods We recorded cortical responses to an electrocutaneous stimulation presented randomly to any of the five fingers of the right hand at a random interstimulus interval (750–1250 ms). Participants attended to the index finger, ring finger, or both to detect a rare target stimulus presented there by silent counting. Results Neuromagnetic responses around the contralateral primary and secondary somatosensory cortices (SIc and SIIc) for the stimulation of the index or middle finger were stronger when that finger was attended than when the distant finger was attended. The SIIc response to the task-irrelevant stimulation of the thumb or little finger increased when the index or ring finger was attended, respectively, suggesting an across-finger gradient of tactile attention. Simultaneous attention to the index and ring fingers decreased the SIIc response to the task-irrelevant stimulation of the intervening middle finger more than that with attention to either one of the two fingers. Furthermore, late responses in the temporo-parietal junction (TPJ) and prefrontal cortex (PFC) were stronger with the stimulation of the unattended finger than with that of the attended finger. Conclusion The present study provides cortical evidence for the adaptive control of the within-hand, across-finger gradient of tactile attention that depends on whether attention is focused on a single finger or divided into non-adjacent different fingers.

P15: Functional properties of the human brain network underlying attentional control

condition included the same seven sessions, but the subjects were instructed to relax without chewing gum in each interval. Somatosensory stimuli were delivered to the second (Go stimuli) or fifth digit (No-go stimuli) of the left hand, and the subjects had to respond by pushing a button with their right thumb as quickly as possible after the Go stimulus. Reaction time (RT) and the standard deviation (SD) were recorded, and the peak amplitude and latency of the somatosensory N140 and P300 components were analyzed. In Mastication, RT was significantly shorter in Post 1, 3, and 6 than Pre. By contrast, the RT in Control did not differ between Pre and the other sessions. The peak amplitude of the Go-N140 in Mastication was significantly larger in Pre than Post 6, but that in Control was significantly larger in Pre than Post 2, 3, 5, and 6. The peak latency of the Go-P300 in Mastication did not change with repeated sessions, but that in Control was significantly longer in Post 4 and 5 than Pre. No effects of Mastication on the peak amplitude and latency of the N140 and P300 were found in the No-go trials. These results suggest that mastication affected ERP waveforms elicited by the “target” stimulus, rather than “non-target” stimulus. In other words, the effect of mastication would be found on response execution processing in Go trials, rather than inhibitory processing in No-go trials. Since the present study prepared a special gum base that was odorless and tasteless, factors of odor and taste could be ruled out. This is the first study to investigate the effect of mastication on Go/No-go decisional processing.

P33-18 Brain dynamics of the visual change detection based on sensory memory

S. Ichihara-Takeda1, S. Yazawa2, T. Murahara2, T. Toyoshima3, J. Shinozaki2, M. Ishiguro2, H. Shiraishi4, K. Matsuyama1, T. Nagamine2 1Department of Occupational Therapy, School of Health Science, Sapporo Medical University, Sapporo, Japan, 2Department of System Neuroscience, School of Medicine, Sapporo Medical University, Sapporo, Japan, 3Department of Neurology, School of Medicine, Sapporo Medical University, Sapporo, Japan, 4Department of Pediatrics, Hokkaido University School of Medicine, Sapporo, Japan