Biomedical subjects

Rodrigo Quian Quiroga

Publications and source records attributed to Rodrigo Quian Quiroga.

12 recordsLinked to original sources

PubMed2006

A single-neuron correlate of change detection and change blindness in the human medial temporal lobe.

Observers are often unaware of changes in their visual environment when attention is not focused at the location of the change . Because of its rather intriguing nature, this phenomenon, known as change blindness, has been extensively studied with psychophysics as well as with fMRI . However, whether change blindness can be tracked in the activity of single cells is not clear. To explore the neural correlates of change detection and change blindness, we recorded from single neurons in the human medial temporal lobe (MTL) during a change-detection paradigm. The preferred pictures of the visually responsive units elicited significantly higher firing rates on the attended trials when subjects correctly identified a change (change detection) compared to the unattended trials when they missed it (change blindness). On correct trials, the firing activity of individual units allowed us to predict the occurrence of a change, on a trial-by-trial basis, with 67% accuracy. In contrast, this prediction was at chance for incorrect, unattended trials. The firing rates of visually selective MTL cells thus constitute a neural correlate of change detection.

Action Potentials↗

PubMed2006

Sparse representation in the human medial temporal lobe.

Recent experiments characterized individual neurons in the human medial temporal lobe with remarkably selective, invariant, and explicit responses to images of famous individuals or landmark buildings. Here, we used a probabilistic analysis to show that these data are consistent with a sparse code in which neurons respond in a selective manner to a small fraction of stimuli.

Models, Neurological↗

PubMed2006

Tracking pattern learning with single-trial event-related potentials.

OBJECTIVE: The main aim was to track the dynamics of pattern-learning using single-trial event-related potentials (ERPs). A new 'learning-oddball' paradigm was employed presenting eight random targets (the 'no-pattern') followed by eight regular targets (the 'pattern'). In total, six repetitions of the 'no-pattern' followed by the 'pattern' were presented. METHODS: We traced the dynamics of learning by measuring responses to 16 (eight random-eight regular) targets. Since this alternation of the 'no-pattern' followed by the 'pattern' was repeated six times, we extracted single-trial responses to all 96 targets to determine if learning occurred more rapidly with each repetition of the 'pattern.' RESULTS: Following random targets, ERPs contained a marked P3-N2 component that decreased to regular targets, whereas a contingent negative variation (CNV) appeared. ERP changes could be best described by sigmoid 'learning' curves. Single-trial analyses showed that learning occurred more rapidly over repetitions and suggested that the CNV developed prior to the decay of the N2-P3 component. CONCLUSIONS: We show a new paradigm-analysis methodology to track learning processes directly from brain signals. SIGNIFICANCE: Single-trial ERPs analyses open a wide range of applications. Tracking the dynamic structure of cognitive functions may prove crucial in the understanding of learning and in the study of different pathologies.

Acoustic Stimulation↗

PubMed2006

Movement intention is better predicted than attention in the posterior parietal cortex.

We decoded on a trial-by-trial basis the location of visual targets, as a marker of the locus of attention, and intentions to reach and to saccade in different directions using the activity of neurons in the posterior parietal cortex of two monkeys. Predictions of target locations were significantly worse than predictions of movement plans for the same target locations. Moreover, neural signals in the parietal reach region (PRR) gave better predictions of reaches than saccades, whereas signals in the lateral intraparietal area (LIP) gave better predictions of saccades than reaches. Taking together the activity of both areas, the prediction of either movement in all directions became nearly perfect. These results cannot be explained in terms of an attention effect and support the idea of two segregated populations in the posterior parietal cortex, PRR and LIP, that are involved in different movement plans.

Animals↗

PubMed2006

Object selectivity of local field potentials and spikes in the macaque inferior temporal cortex.

Local field potentials (LFPs) arise largely from dendritic activity over large brain regions and thus provide a measure of the input to and local processing within an area. We characterized LFPs and their relationship to spikes (multi and single unit) in monkey inferior temporal cortex (IT). LFP responses in IT to complex objects showed strong selectivity at 44% of the sites and tolerance to retinal position and size. The LFP preferences were poorly predicted by the spike preferences at the same site but were better explained by averaging spikes within approximately 3 mm. A comparison of separate sites suggests that selectivity is similar on a scale of approximately 800 microm for spikes and approximately 5 mm for LFPs. These observations imply that inputs to IT neurons convey selectivity for complex shapes and that such input may have an underlying organization spanning several millimeters.

Action Potentials↗

PubMed2005

Assessing the spatiotemporal evolution of neuronal activation with single-trial event-related potentials and functional MRI.

The brain acts as an integrated information processing system, which methods in cognitive neuroscience have so far depicted in a fragmented fashion. Here, we propose a simple and robust way to integrate functional MRI (fMRI) with single trial event-related potentials (ERP) to provide a more complete spatiotemporal characterization of evoked responses in the human brain. The idea behind the approach is to find brain regions whose fMRI responses can be predicted by paradigm-induced amplitude modulations of simultaneously acquired single trial ERPs. The method was used to study a variant of a two-stimulus auditory target detection (odd-ball) paradigm that manipulated predictability through alternations of stimulus sequences with random or regular target-to-target intervals. In addition to electrophysiologic and hemodynamic evoked responses to auditory targets per se, single-trial modulations were expressed during the latencies of the P2 (170-ms), N2 (200-ms), and P3 (320-ms) components and predicted spatially separated fMRI activation patterns. These spatiotemporal matches, i.e., the prediction of hemodynamic activation by time-variant information from single trial ERPs, permit inferences about regional responses using fMRI with the temporal resolution provided by electrophysiology.

Adult↗

PubMed2005

Nonlinear multivariate analysis of neurophysiological signals.

Multivariate time series analysis is extensively used in neurophysiology with the aim of studying the relationship between simultaneously recorded signals. Recently, advances on information theory and nonlinear dynamical systems theory have allowed the study of various types of synchronization from time series. In this work, we first describe the multivariate linear methods most commonly used in neurophysiology and show that they can be extended to assess the existence of nonlinear interdependence between signals. We then review the concepts of entropy and mutual information followed by a detailed description of nonlinear methods based on the concepts of phase synchronization, generalized synchronization and event synchronization. In all cases, we show how to apply these methods to study different kinds of neurophysiological data. Finally, we illustrate the use of multivariate surrogate data test for the assessment of the strength (strong or weak) and the type (linear or nonlinear) of interdependence between neurophysiological signals.

Action Potentials↗

PubMed2005

Expectancy effects on omission evoked potentials in musicians and non-musicians.

Abstract An expanded omitted stimulus paradigm was investigated to determine whether expectancy would modulate the amplitude of the omission evoked potentials (OEPs). In addition, we examined the effects of musical expertise on OEPs. Trials started with 3-7 beats randomly and contained 5 omitted beats. Three types of trials (n = 90) were presented with 1, 2, or 3 beats occurring between omissions. A tap response at the end of each trial was used to determine timing accuracy. Clear OEPs were observed over midline sites. We found main omission effects with respect to an N150 and a P400 OEPs component, such that peak amplitudes diminished whenever the occurrence of an omitted stimulus could be expected. In addition, an N600 OEPs component emerged in response to expectedly omitted stimuli toward the end of each trial within the group of musicians. Thus, musical training seems to lead to more efficient and more refined processing of auditory temporal patterns.

Adult↗

PubMed2004

Spatio-temporal frequency characteristics of intersensory components in audiovisually evoked potentials.

Perception of the external world is based on complex neural processes allowing for combination of sensory experiences from different modalities. Audiovisual (AV) integration is discussed in this paper on the basis of the intersensory component (IC), which is the part of the multisensory-evoked potential that is not explained by linear summation of the unisensory-evoked potentials. It was predicted that audiovisual ICs can be extracted, localized, and differentiated by means of wavelet-based frequency analysis. Healthy, right-handed subjects (n = 15) were instructed to view and listen to presented stimuli (A: auditory; V: visual; and AV: audiovisual). Electroencephalographic data was analyzed off-line by means of wavelet transformation utilizing quadratic B-spline mother wavelets. Cross-modal interaction was investigated by subtracting wavelet responses to unimodal stimuli (A, V) alone from the wavelet responses to the combined stimuli (AV; i.e., interaction = AV - (A + V)). These difference waveforms revealed the phase-locked fraction of ICs further characterized by frequency-band and location. Spatio-temporally distinct ICs were observed in all frequency bands [31-62 Hz (gamma), 16-31 Hz (beta), 8-16 Hz (alpha), 4-8 Hz (theta), 0.5-4 Hz band (delta)]. These were most pronounced and sustained in the theta frequency band with early (<100 ms) appearance in fronto-centro-parietal sites. In contrast, alpha-band ICs tended to appear later (>200 ms) in these locations. High-frequency (beta- and gamma-band) ICs were less organized in their spatial pattern with both early and late appearance. ICs may reflect sensory and cognitive/integrative processes at the cortical level. In case of intersensory processing, alpha- and theta-activity appear to be spatio-temporally distinct, and could therefore participate in different stages of perception. These findings add further support to current model views of oscillatory activity in selectively distributed networks.

Adult↗

PubMed2004

Rhythmic training decreases latency-jitter of omission evoked potentials (OEPs) in humans.

In this study omission evoked potentials (OEPs) were studied in rhythmic experts (n=12) and non-musicians (n=12). Trains of auditory stimuli were presented. Trials (n=90) contained five omissions and started with a random number of beats, thus making every first omission unpredictable. Participants had to tap along with the first beat after the fifth omission (n=90), thus determining timing-accuracy. Single-trial OEPs elicited by every first omission were obtained by means of wavelet denoising allowing determination of latency-jitter. Clear OEPs, consisting of a slow positive wave, maximal over Pz, were observed in response to unpredictable omissions. No group differences in OEPs amplitudes or latencies were observed. However, rhythmic experts showed less latency-jitter of both the OEPs positive wave and of behavioral responses compared with non-musicians.

Acoustic Stimulation↗

PubMed2004

Effects of stimulus repetitions on the event-related potential of humans and rats.

The present study compared the effects of repeated stimulus presentations on the event-related potential (ERP) of humans and rats. Both species were presented with a total of 100 auditory stimuli, divided into four blocks of 25 stimuli. By means of wavelet denoising, single-trial ERPs were established in both humans and rats. The auditory ERPs were characterized by the presence of two positive and two negative waves in both humans and rats, albeit with different latencies in the two species (P1, N1, P2, and N2). The results showed decreased amplitudes within blocks for the N1, P2, and N2 components in humans and for the N1 and P2 components in rats. Decreased amplitudes across blocks were found for the N2 component in humans and for the P2 and N2 components in rats. In both humans and rats, response decrements within a block were thus most prominent for the early ERP components, whereas the changes across blocks were most prominent for the later components. These results suggest a correspondence of the ERP correlates of elemental stimulus processing between humans and rats. It is further suggested that the observed amplitude reductions may reflect habituation and/or recovery cycle processes.

Acoustic Stimulation↗

PubMed2003

Entorhinal inputs to dentate gyrus are activated mainly by conditioned events with long time intervals.

Brain mechanisms of mammalian learning and memory have long been associated with the hippocampus. Although the role of the hippocampus in spatial behavior is well established, there is no general consensus on the function of the hippocampus in nonspatial tasks. Task-related changes in evoked potentials were first reported by Deadwyler and colleagues in the dentate gyrus, with a peak at 100 ms in rats trained in an auditory discrimination task (Deadwyler et al., Brain Res 161:211-225, 1979). Surprisingly, these results have not been confirmed by other investigators. In the present report, we set out to assess the task parameters that induce, modulate, and suppress this potential. Using multielectrode probes and current source density analysis, we monitored the entorhinal input to the dentate gyrus in behaving rats. Both differential and simple auditory conditioning led to the appearance of a large negative potential at 100 ms in the perforant path zone of the dentate gyrus. This negativity was found in averaged and in single-trial, evoked potentials. Current source density analysis revealed sinks in the perforant path zone of the molecular layer of the dentate gyrus with corresponding sources in the hilus. Once trained for differential conditioning, decrements of target probability consistently increased the amplitude of this negativity. When using a single-tone, stimulus-response task, the negative potential occurred with long (70-s), but not with short (10-s) intertrial intervals. Appearance of the potential coincided with a switch in response strategy and disappeared under stereotypical behavior. These data are best explained under the assumption that long intertrial intervals lead to transitions in task-related reference frames enabling a switch to more appropriate response strategies. Such transitions are not required during short interval stereotyped performance.

Acoustic Stimulation↗