Cross-frequency coupling of brain oscillations indicates the success in visual motion discrimination

Cortical activity such as recorded by EEG or MEG is characterized by ongoing rhythms that encompass a wide range of temporal and spatial scales. Recent studies have suggested an oscillatory hierarchy with faster oscillations being locked to preferred phases of underlying slower waves, a functional principle applied up to the level of action potential generation. We here tested the idea that amplitude-phase coupling between frequencies might serve the detection of weak sensory signals. To this end we recorded neuromagnetic responses during a motion discrimination task using near-threshold stimuli. Amplitude modulation of occipital high-frequency oscillations in the gamma range (63+/-5 Hz) was phase locked to a slow-frequency oscillation in the delta band (1-5 Hz). Most importantly, the strength of gamma amplitude modulation reflected the success in visual discrimination. This correlation provides evidence for the hypothesis that coupling between low- and high-frequency brain oscillations subserves signal detection

Visual motion perception deficits due to cerebellar lesions are paralleled by specific changes in cerebro-cortical activity

Recent anatomical studies have revealed strong cerebellar projections into parietal and prefrontal cortex. These findings suggest that the cerebellum might not only play a functional role in motor control but also cognitive domains, an idea also supported by neuropsychological testing of patients with cerebellar lesions that has revealed specific deficits. The goal of the present study was to test whether or not cognitive impairments after cerebellar damage are resulting from changes in cerebro-cortical signal processing. The detection of global visual motion embedded in noise, a faculty compromised after cerebellar lesions, was chosen as a model system. Using magnetoencephalography, cortical responses were recorded in a group of patients with cerebellar lesions (n = 8) and controls (n = 13) who observed visual motion of varied coherence, i.e., motion strength, presented in the peripheral visual field during controlled stationary fixation. Corroborating earlier results, the patients showed a significant impairment in global motion discrimination despite normal fixation behavior. This deficit was paralleled by qualitative differences in responses recorded from parieto-temporal cortex, including a reduced responsiveness to coherent visual motion and a striking loss of bilateral representations of motion coherence. Moreover, the perceptual thresholds correlated with the cortical representation of motion strength on single subject basis. These results demonstrate that visual motion processing in cerebral cortex critically depends on an intact cerebellum and establish a correlation between cortical activity and impaired visual perception resulting from cerebellar damage

Real color captures attention and overrides spatial cues in grapheme-color synesthetes but not in controls

Item does not contain fulltextGrapheme-color synesthetes perceive color when reading letters or digits. We investigated oscillatory brain signals of synesthetes vs. controls using magnetoencephalography. Brain oscillations specifically in the alpha band (∼10 Hz) have two interesting features: alpha has been linked to inhibitory processes and can act as a marker for attention. The possible role of reduced inhibition as an underlying cause of synesthesia, as well as the precise role of attention in synesthesia is widely discussed. To assess alpha power effects due to synesthesia, synesthetes as well as matched controls viewed synesthesia-inducing graphemes, colored control graphemes, and non-colored control graphemes while brain activity was recorded. Subjects had to report a color change at the end of each trial which allowed us to assess the strength of synesthesia in each synesthete. Since color (synesthetic or real) might allocate attention we also included an attentional cue in our paradigm which could direct covert attention. In controls the attentional cue always caused a lateralization of alpha power with a contralateral decrease and ipsilateral alpha increase over occipital sensors. In synesthetes, however, the influence of the cue was overruled by color: independent of the attentional cue, alpha power decreased contralateral to the color (synesthetic or real). This indicates that in synesthetes color guides attention. This was confirmed by reaction time effects due to color, i.e. faster RTs for the color side independent of the cue. Finally, the stronger the observed color dependent alpha lateralization, the stronger was the manifestation of synesthesia as measured by congruency effects of synesthetic colors on RTs. Behavioral and imaging results indicate that color induces a location-specific, automatic shift of attention towards color in synesthetes but not in controls. We hypothesize that this mechanism can facilitate coupling of grapheme and color during the development of synesthesia

Otto Loth's letter to Ignaz Goldziher

Abstract. While a BCI usually aims to provide an alternative communication channel for disabled users who have difficulties to move or to speak, we focused on BCIs as a way to retrieve and use information about an individual’s cognitive or affective state without requiring any effort or intention of the user to convey this information. Providing only an extra channel of information rather than a replacement of certain functions, such BCIs could be useful for healthy users as well. We describe the results of our studies on neurophysiological correlates of attention, workload and emotion, as well as our efforts to include physiological variables. We found different features in EEG to be indicative of attention and workload, while emotional state may be better measured by physiological variables like heart rate and skin conductance. Potential applications are described. We argue that major challenges lie in hardware and generalization issues