1,128 research outputs found
Visual modulation of neurons in auditory cortex
No full textKayser C, Petkov CI, Logothetis NK. Visual modulation of neurons in auditory cortex. Cereb Cortex. 2008;18(7):1560-74
Tuning to sound frequency in auditory field potentials
No full textKayser C, Petkov CI, Logothetis NK. Tuning to sound frequency in auditory field potentials. J Neurophysiol. 2007;98(3):1806-9
Parametric study of EEG sensitivity to phase noise during face processing
No full text<b>Background: </b>
The present paper examines the visual processing speed of complex objects, here faces, by mapping the relationship between object physical properties and single-trial brain responses. Measuring visual processing speed is challenging because uncontrolled physical differences that co-vary with object categories might affect brain measurements, thus biasing our speed estimates. Recently, we demonstrated that early event-related potential (ERP) differences between faces and objects are preserved even when images differ only in phase information, and amplitude spectra are equated across image categories. Here, we use a parametric design to study how early ERP to faces are shaped by phase information. Subjects performed a two-alternative force choice discrimination between two faces (Experiment 1) or textures (two control experiments). All stimuli had the same amplitude spectrum and were presented at 11 phase noise levels, varying from 0% to 100% in 10% increments, using a linear phase interpolation technique. Single-trial ERP data from each subject were analysed using a multiple linear regression model.
<b>Results: </b>
Our results show that sensitivity to phase noise in faces emerges progressively in a short time window between the P1 and the N170 ERP visual components. The sensitivity to phase noise starts at about 120–130 ms after stimulus onset and continues for another 25–40 ms. This result was robust both within and across subjects. A control experiment using pink noise textures, which had the same second-order statistics as the faces used in Experiment 1, demonstrated that the sensitivity to phase noise observed for faces cannot be explained by the presence of global image structure alone. A second control experiment used wavelet textures that were matched to the face stimuli in terms of second- and higher-order image statistics. Results from this experiment suggest that higher-order statistics of faces are necessary but not sufficient to obtain the sensitivity to phase noise function observed in response to faces.
<b>Conclusion: </b>
Our results constitute the first quantitative assessment of the time course of phase information processing by the human visual brain. We interpret our results in a framework that focuses on image statistics and single-trial analyses
Fixations in natural scenes: interaction of image structure and image content
No full textKayser C, Nielsen KJ, Logothetis NK. Fixations in natural scenes: interaction of image structure and image content. Vision Res. 2006;46(16):2535-45
Functional imaging reveals visual modulation of specific fields in auditory cortex
No full textKayser C, Petkov CI, Augath M, Logothetis NK. Functional imaging reveals visual modulation of specific fields in auditory cortex. Journal of Neuroscience. 2007;27(8):1824-35
Multisensory Influences on Auditory Processing: Perspectives from fMRI and Electrophysiology
No full textKayser C, Petkov CI, Remedios R, Logothetis NK. Multisensory Influences on Auditory Processing: Perspectives from fMRI and Electrophysiology. In: Murray MM, Wallace MT, eds. The Neural Bases of Multisensory Processes. Boca Raton FL: Llc.; 2012
Simultaneous recording of neuronal signals and functional NMR imaging
No full textWe recently directly examined the relationship between blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) signals and neural activity by simultaneously acquiring electrophysiological and fMRI data from monkeys in a 4.7-T vertical scanner (Logothetis NK, Pauls J, Augath MA, Trinath T, Oeltermann A. Neurophysiological investigation of the basis of the fMRI signal. Nature 2001;412:150157). Acquisition of electrical signals in the microvolt range required extensive development of new recording hardware, including electrodes, microdrives, signal conditioning and interference compensation devices. Here, we provide a detailed description of the interference compensation system that can be used to record field and action potentials intracortically within a high-field scanner
Optimal Band Separation of Extracellular Field Potentials
No full textLocal Field Potentials (LFPs) exhibit a broadband spectral structure that is traditionally partitioned into distinct frequency bands which are thought to originate from different types of neural events triggered by different processing pathways. However, the exact frequency boundaries of these processes are not known and, as a result, the frequency bands are often selected based on intuition, previous literature or visual inspection of the data. Here, we address these problems by developing a rigorous method for defining LFP frequency bands and their boundaries. The criterion introduced for determining the boundaries delimiting the bands is to maximize the information about an external correlate carried jointly by all bands in the partition. The method first partitions the LFP frequency range into two bands and then successively increases the number of bands in the partition. We applied the partitioning method to LFPs recorded from primary visual cortex of anaesthetized macaques, and we determined the optimal band partitioning that describes the encoding of naturalistic visual stimuli. The first optimal boundary partitioned the LFP response at 60 Hz into low and high frequencies, which had been previously found to convey independent information about the natural movie correlate. The second optimal boundary divided the high-frequency range at approximately 100 Hz into gamma and high-gamma frequencies, consistent with recent reports that these two bands reflect partly distinct neural processes. A third important boundary was at 25 Hz and it split the LFP range below 50 Hz into a stimulus-informative and a stimulus-independent band
Multimodal contrast agents for in vivo neuroanatomical analysis of monosynaptic connections
No full textWe developed and examined the applicability of two multimodal paramagnetic contrast agents for the
longitudinal in vivo investigations of the brain projections. The classical dextran based neuroanatomical
tracer was conjugated with mono- and bimetal Gd3þ complexes and an optical reporter. Relaxometric
studies of both tracer molecules were performed in vitro followed by in cellulo MR and microscopy investigations. Finally, tracers were injected into the motor cortex of the rat brain; uptake and transporting
properties were compared by MRI. The advantage of the multimodal approach was taken and histological studies were performed on the same animals. The histology results confirm the MRI studies demonstrating that the applied tracers labelled anterogradely the regions known for their connections with the motor cortex of the rat brain
Neurons with stereotyped and rapid responses provide a reference frame for relative temporal coding in primate auditory cortex
No full textThe precise timing of spikes of cortical neurons relative to stimulus onset carries substantial sensory information. To access this information the sensory systems would need to maintain an internal temporal reference that reflects the precise stimulus timing. Whether and how sensory systems implement such reference frames to decode time-dependent responses, however, remains debated. Studying the encoding of naturalistic sounds in primate (Macaca mulatta) auditory cortex we here investigate potential intrinsic references for decoding temporally precise information. Within the population of recorded neurons, we found one subset responding with stereotyped fast latencies that varied little across trials or stimuli, while the remaining neurons had stimulus-modulated responses with longer and variable latencies. Computational analysis demonstrated that the neurons with stereotyped short latencies constitute an effective temporal reference for relative coding. Using the response onset of a simultaneously recorded stereotyped neuron allowed decoding most of the stimulus information carried by onset latencies and the full spike train of stimulus-modulated neurons. Computational modeling showed that few tens of such stereotyped reference neurons suffice to recover nearly all information that would be available when decoding the same responses relative to the actual stimulus onset. These findings reveal an explicit neural signature of an intrinsic reference for decoding temporal response patterns in the auditory cortex of alert animals. Furthermore, they highlight a role for apparently unselective neurons as an early saliency signal that provides a temporal reference for extracting stimulus information from other neurons
- …
