Attentional modulation of oscillatory activity in human visual cortex

Abstract

The effects of attentional modulation on activity within the human visual cortex were investigated using magnetoencephalography. Chromatic sinusoidal stimuli were used to evoke activity from the occipital cortex, with attention directed either toward or away from the stimulus using a bar-orientation judgment task. For five observers, global magnetic field power was plotted as a function of time from stimulus onset. The major peak of each function occurred at about 120 ms latency and was well modeled by a current dipole near the calcarine sulcus. Independent component analysis (ICA) on the non-averaged data for each observer also revealed one component of calcarine origin, the location of which matched that of the dipolar source determined from the averaged data. For two observers, ICA revealed a second component near the parieto-occipital sulcus. Although no effects of attention were evident using standard averaging procedures, time-varying spectral analyses of single trials revealed that the main effect of attention was to alter the level of oscillatory activity. Most notably, a sustained increase in alpha-band (7-12 Hz) activity of both calcarine and parieto-occipital origin was evident. In addition, calcarine activity in the range of 13-21 Hz was enhanced, while calcarine activity in the range of 5-6 Hz was reduced. Our results are consistent with the hypothesis that attentional modulation affects neural processing within the calcarine and parieto-occipital cortex by altering the amplitude of alpha-band activity and other natural brain rhythms.

α-Band Electroencephalographic Activity over Occipital Cortex Indexes Visuospatial Attention Bias and Predicts Visual Target Detection

“…In further analogy to Sauseng et al (2005), we found ␣ activity to be significantly suppressed relative to the precue period at sites contralateral to the attended visual hemifield, but did not find any significant increase in the level of oscillatory ␣ activity contralateral to unattended space. This contrasts with previous reports of sustained focal ␣ increases at parieto-occipital sites contralateral to the to-be-ignored position (Worden et al, 2000;Yamagishi et al, 2003;Kelly et al, 2006). However, although divergent, ␣ increases and decreases are not mutually exclusive and might become expressed to different degrees depending on task demand, as suggested previously (Kelly et al, 2006).…”

“…In the case of visuospatial attention deployment, decreases of ␣-activity have been observed contralateral to the attended location (Sauseng et al, 2005), interpreted to reflect enhanced cortical excitability to facilitate future visual processing at the attended position. In addition, ␣ increases have been documented contralateral to the unattended location (Worden et al, 2000;Yamagishi et al, 2003;Kelly et al, 2006), potentially reflecting an active "inhibitory" process protecting against visual input from task-irrelevant positions. Based on these results, it may be suggested that the direction of visuospatial attention is determined by two divergent processes that are reflected in differential changes of ␣ activity over the two hemispheres (facilitatory ␣ decrease and inhibitory ␣ increase over areas tuned to the attended vs unattended hemifields).…”

Early Neural Correlates of Conscious Somatosensory Perception

“…For a 10 Hz wavelet, the time-domain SD ( t ) is 87.5 ms, and the time-domain envelope half-width at half-height is 103 ms (cf. Yamagishi et al, 2003). For the broadband filter, the half-width at half-height is 10.4 ms.…”

“…A recent MEG study showed that the amplitude of early (ϳ0 -200 ms after stimulus onset) ␣ oscillations in the visual cortex is larger for the attended than for the unattended stimuli (Yamagishi et al, 2003). In addition, stimulus-and nonstimulus-locked ␣-band oscillations are stronger during short-term memory retention than during baseline in intracranial (Halgren et al, 2002) and MEG (Jensen et al, 2002) recordings.…”

Simultaneous recordings of visual evoked potentials and BOLD MRI activations in response to visual motion processing

“…The use of simultaneous EEG and BOLD MRI recordings largely eliminated confounding factors such as attentional shifts that would be evident for separate EEG and neuroimaging sessions (11,(22)(23)(24)(25)(26)(27)(28). In more detail, the present study not only included comparisons of motion stimuli with stationary dot patterns of equal overall luminance and contrast, but also differential paradigms contrasting motion stimuli against each other.…”