Lucas C Parra

Lucas C Parra
City College of New York | CCNY · Department of Biomedical Engineering

PhD

About

305
Publications
44,819
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13,974
Citations
Additional affiliations
July 2003 - present
City College of New York
Position
  • Professor

Publications

Publications (305)
Preprint
Full-text available
Our continuous visual experience in daily life is dominated by change. Previous research has focused on the effects of visual motion, eye movements or the transition between events, but has failed to capture their full impact across the brain. Using intracranial recordings in humans, we investigate the neural responses to these sources of novelty d...
Article
Neural, physiological and behavioral signals synchronize between human subjects in a variety of settings. Multiple hypotheses have been proposed to explain this interpersonal synchrony, but there is no clarity under which conditions it arises, for which signals, or whether there is a common underlying mechanism. We hypothesized that similar cogniti...
Article
Full-text available
Background Electric fields generated during direct current stimulation (DCS) are known to modulate activity-dependent synaptic plasticity in-vitro. This provides a mechanistic explanation for the lasting behavioral effects observed with transcranial direct current stimulation (tDCS) in human learning experiments. However, previous in-vitro synaptic...
Chapter
Noninvasive brain stimulation techniques, including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), are customized to experimental and clinical applications based on their presumed mechanism of action, which derive largely from insights in animal models. At the same time, human testing has in...
Chapter
Experimentations with animal models spanning decades have characterized a number of effects of weak electric stimulation (ES) on neurons and brain activity. By “weak,” we mean electric fields that are too weak to activate otherwise quiescent neurons. Low-intensity (few mA) transcranial electrical stimulation (tES) produces weak electric fields in t...
Preprint
Full-text available
Neural, physiological and behavioral signals synchronize between human subjects in a variety of settings. Multiple hypotheses have been proposed to explain this interpersonal synchrony, but there is no clarity under which conditions it arises, for which signals, or whether there is a common underlying mechanism. We hypothesized that similar cogniti...
Article
Full-text available
Relatively little is known about visual processing during free-viewing visual search in realistic dynamic environments. Free-viewing is characterized by frequent saccades. During saccades, visual processing is thought to be suppressed, yet we know that the presaccadic visual content can modulate postsaccadic processing. To better understand these p...
Article
Full-text available
Heart rate has natural fluctuations that are typically ascribed to autonomic function. Recent evidence suggests that conscious processing can affect the timing of the heartbeat. We hypothesized that heart rate is modulated by conscious processing and therefore dependent on attentional focus. To test this, we leverage the observation that neural pro...
Article
Full-text available
Background Skin sensation is the primary factor limiting the intensity of transcranial electrical stimulation (tES). It is well established that different waveforms generate different sensations, yet transcranial stimulation has been limited to a relatively small number of prototypical waveforms. Objective We explore whether alternative stimulatio...
Article
Full-text available
It is well established that neural responses to visual stimuli are enhanced at select locations in the visual field. While spatial selectivity and the effects of spatial attention are well‐understood for discrete tasks (e.g., visual cueing), little is known for naturalistic experience that involves continuous dynamic visual stimuli (e.g., driving)....
Preprint
It is well established that neural responses to visual stimuli are enhanced at select locations in the visual field. While spatial selectivity and the effects of spatial attention are well-understood for discrete tasks (e.g., visual cueing paradigms), little is known about neural response during a naturalistic visual experience that involves comple...
Article
Impaired inhibitory control accompanied by enhanced salience attributed to drug‐related cues, both associated with function of the dorsolateral prefrontal cortex (dlPFC), are hallmarks of drug addiction, contributing to worse symptomatology including craving. dlPFC modulation with transcranial direct current stimulation (tDCS) previously showed cra...
Article
Full-text available
Background Transcranial direct current stimulation (DCS) has lasting effects that may be explained by a boost in synaptic long-term potentiation (LTP). We hypothesized that this boost is the result of a modulation of somatic spiking in the postsynaptic neuron, as opposed to indirect network effects. To test this directly we record somatic spiking i...
Preprint
Full-text available
Relatively little is known about visual processing during free-viewing visual search in realistic dynamic environments. Free-viewing is characterized by frequent saccades. During saccades, visual processing is thought to be inhibited, yet we know that the pre-saccadic visual content can modulate post-saccadic processing. To better understand these...
Article
Significance Education is increasingly delivered online, but are students actually paying attention? Here we demonstrate that efficacy of video instruction can be assessed remotely with standard web cameras. Specifically, we show that attentive students have similar eye movements when watching instructional videos and that synchronization of eye mo...
Article
Full-text available
Background Temporal interference (TI) stimulation of the brain generates amplitude-modulated electric fields oscillating in the kHz range with the goal of non-invasive targeted deep brain stimulation. Yet, the current intensities required in human (sensitivity) to modulate deep brain activity and if superficial brain region are spared (selectivity)...
Preprint
Full-text available
Impaired inhibitory control accompanied by enhanced salience attributed to drug-related cues, both dorsolateral prefrontal cortex (dlPFC) functions, are hallmarks of drug addiction, contributing to worse symptomatology including craving. dlPFC modulation with transcranial direct current stimulation (tDCS) showed craving reduction in inpatients with...
Article
Full-text available
While it is well known that vision guides movement, less appreciated is that the motor cortex also provides input to the visual system. Here we asked whether neural processing of visual stimuli is acutely modulated during motor activity, hypothesizing that visual evoked responses are enhanced when engaged in a motor task that depends on the visual...
Article
Full-text available
Odors can be powerful stimulants. It is well-established that odors provide strong cues for recall of locations, people and events. The effects of specific scents on other cognitive functions are less well-established. We hypothesized that scents with different odor qualities will have a different effect on attention. To assess attention, we used I...
Preprint
Heart rate has natural fluctuations that are typically ascribed to autonomic function. Recent evidence suggests that conscious processing can affect the timing of the heartbeat. We hypothesized that heart rate is modulated by conscious processing and therefore dependent on attentional focus. To test this we leverage the observation that neural proc...
Article
Objective: Interferential stimulation (IFS) has generated considerable interest recently because of its potential to achieve focal electric fields in deep brain areas with transcranial currents. Conventionally, IFS applies sinusoidal currents through two electrode pairs with close-by frequencies. Here we propose to use an array of electrodes inste...
Article
Full-text available
A variety of psychiatric, behavioral and cognitive phenotypes have been linked to brain ‘’functional connectivity’’ -- the pattern of correlation observed between different brain regions. Most commonly assessed using functional magnetic resonance imaging (fMRI), here, we investigate the connectivity-phenotype associations with functional connectivi...
Article
Full-text available
Despite being a popular neuromodulation technique, clinical translation of transcranial direct current stimulation (tDCS) is hampered by variable responses observed within treatment cohorts. Addressing this challenge has been difficult due to the lack of an effective means of mapping the neuromodulatory electromagnetic fields together with the brai...
Preprint
Full-text available
Temporal interference (TI) stimulation of the brain generates amplitude-modulated electric fields oscillating in the kHz range. A validated current-flow model of the human head estimates that amplitude-modulated electric fields are stronger in deep brain regions, while unmodulated electric fields are maximal at the cortical regions. The electric fi...
Preprint
Full-text available
Experienced teachers pay close attention to their students, adjusting their teaching when students seem lost. This dynamic interaction is missing in online education. We propose to measure attention to online videos remotely by tracking eye movements, as we hypothesize that attentive students follow videos similarly with their eyes. Here we show th...
Article
Full-text available
Slow oscillations and spindle activity during non-rapid eye movement sleep have been implicated in memory consolidation. Closed-loop acoustic stimulation has previously been shown to enhance slow oscillations and spindle activity during sleep and improve verbal associative memory. We assessed the effect of closed-loop acoustic stimulation during a...
Article
Background There is evidence that transcranial direct current stimulation (tDCS) can improve learning performance. Arguably, this effect is related to long term potentiation (LTP), but the precise biophysical mechanisms remain unknown. Hypothesis We propose that direct current stimulation (DCS) causes small changes in postsynaptic membrane potenti...
Preprint
Full-text available
Objective Interferential stimulation (IFS) has generated considerable interest recently because of its potential to achieve focal electric fields in deep brain areas with transcranial currents. Conventionally, IFS applies sinusoidal currents through two electrode pairs with close-by frequencies. Here we propose to use an array of electrodes instead...
Article
Objective: Research in the area of transcranial electrical stimulation (TES) often relies on computational models of current flow in the brain. Models are built based on magnetic resonance images (MRI) of the human head to capture detailed individual anatomy. To simulate current flow on an individual, the subject's MRI is segmented, virtual electr...
Preprint
Full-text available
Research in the area of transcranial electrical stimulation (TES) often relies on computational models of current flow in the brain. Models are built on magnetic resonance images (MRI) of the human head to capture detailed individual anatomy. To simulate current flow, MRIs have to be segmented, virtual electrodes have to be placed on these anatomic...
Article
Full-text available
Costly signaling theory was developed in both economics and biology and has been used to explain a wide range of phenomena. However, the theory’s prediction that signal cost can enforce information quality in the design of new communication systems has never been put to an empirical test. Here we show that imposing time costs on reporting extreme s...
Preprint
Full-text available
While it is well known that vision guides movement, it is less appreciated that motor cortex also provides input to the visual system. Here we asked whether neural processing of visual stimuli is acutely modulated during motor activity, hypothesizing that visual evoked responses are enhanced when subjects engage in a motor task. To test this, we re...
Article
Full-text available
Music tends to be highly repetitive, both in terms of musical structure and in terms of listening behavior, yet little is known about how engagement changes with repeated exposure. Here we postulate that engagement with music affects the inter-subject correlation of brain responses during listening. We predict that repeated exposure to music will a...
Preprint
Full-text available
There is evidence that transcranial direct current stimulation can boost learning performance. Arguably, this boost is related to synaptic plasticity. However, the precise effects on synaptic plasticity and its underlying mechanisms are not known. We hypothesized that direct current stimulation modulates endogenous Hebbian plasticity mechanisms due...
Article
Objective: Speech signals have a remarkable ability to entrain brain activity to the rapid fluctuations of speech sounds. For instance, one can readily measure a correlation of the sound amplitude with the evoked responses of the electroencephalogram (EEG), and the strength of this correlation is indicative of whether the listener is attending to...
Article
In proportional myographic control one can control either position or velocity of movement. Here we propose to use adaptive auto-regressive filters, so as to gradually adjust between the two. We implemented this in an adaptive system with closed-loop feedback, where both the user and the machine simultaneously attempt to follow a cursor on a two-di...
Article
Full-text available
Noninvasive brain stimulation techniques are used in experimental and clinical fields for their potential effects on brain network dynamics and behavior. Transcranial electrical stimulation (TES), including transcranial direct current stimulation (tDCS) and transcranial alternating current stimulation (tACS), has gained popularity because of its co...
Article
Online imaging and neuromodulation is invalid if stimulation distorts measurements beyond the point of accurate measurement. In theory, combining transcranial Direct Current Stimulation (tDCS) with electroencephalography (EEG) is compelling, as both use non-invasive electrodes and image-guided dose can be informed by the reciprocity principle. To d...
Article
Full-text available
The original version of this Article contained an error in the last sentence of the first paragraph of the Introduction, which incorrectly read 'Correlation of brain activity is typically measured using functional magnetic resonance imaging (fMRI), and the correlation structure is often referred to as "fu'. The correct version states 'referred to a...
Conference Paper
Transcranial direct current stimulation (tDCS) aims to deliver weak electric current into the brain to modulate neural activities. Based on the volume conductor model of the head, optimization algorithm can be used to determine a specific montage of high-definition electrodes on the scalp to achieve targeted stimulation. However, simultaneous targe...
Conference Paper
Research in the area of transcranial electrical stimulation (TES) often relies on computational models of current flow in the brain. Models are built on magnetic resonance images (MRI) of the human head to capture detailed individual anatomy. To simulate current flow, MRIs have to be segmented, virtual electrodes have to be placed on the scalp, the...
Article
Full-text available
Global integration of information in the brain results from complex interactions of segregated brain networks. Identifying the most influential neuronal populations that efficiently bind these networks is a fundamental problem of systems neuroscience. Here, we apply optimal percolation theory and pharmacogenetic interventions in vivo to predict and...
Preprint
Full-text available
Online educational materials are largely disseminated through videos, and yet there is little understanding of how these videos engage students and fuel academic success. We hypothesized that components of the electroencephalogram (EEG), previously shown to reflect video engagement, would be predictive of academic performance in the context of educ...
Article
Human brain mapping relies heavily on fMRI, ECoG and EEG, which capture different physiological signals. Relationships between these signals have been established in the context of specific tasks or during resting state, often using spatially confined concurrent recordings in animals. But it is not certain whether these correlations generalize to o...
Article
Online educational materials are largely disseminated through videos, and yet there is little understanding of how these videos engage students and fuel academic success. We hypothesized that components of the electroencephalogram (EEG), previously shown to reflect video engagement, would be predictive of academic performance in the context of educ...
Article
Full-text available
It has come to our attention that we did not specify whether the stimulation magnitudes we report in this Article are peak amplitudes or peak-to-peak. All references to intensity given in mA in the manuscript refer to peak-to-peak amplitudes, except in Fig. 2, where the model is calibrated to 1 mA peak amplitude, as stated. In the original version...
Article
There are a multitude of methods to perform multi-set correlated component analysis (MCCA), including some that require iterative solutions. The methods differ on the criterion they optimize and the constraints placed on the solutions. This note focuses perhaps on the simplest version, which can be solved in a single step as the eigenvectors of mat...
Article
Full-text available
How does one find data dimensions that are reliably expressed across repetitions? For example, in neuroscience one may want to identify combinations of brain signals that are reliably activated across multiple trials or subjects. For a clinical assessment with multiple ratings, one may want to identify an aggregate score that is reliably reproduced...
Article
Full-text available
Technological and methodological innovations are equipping researchers with unprecedented capabilities for detecting and characterizing pathologic processes in the developing human brain. As a result, ambitions to achieve clinically useful tools to assist in the diagnosis and management of mental health and learning disorders are gaining momentum....
Article
Full-text available
It is said that we lose track of time - that “time flies” - when we are engrossed in a story. How does engagement with the story cause this distorted perception of time, and what are its neural correlates? People commit both time and attentional resources to an engaging stimulus. For narrative videos, attentional engagement can be represented as th...
Article
Full-text available
Background: Neuropsychiatric disorders are a leading source of disability and require novel treatments that target mechanisms of disease. As such disorders are thought to result from aberrant neuronal circuit activity, neuromodulation approaches are of increasing interest given their potential for manipulating circuits directly. Low intensity tran...
Article
Full-text available
Transcranial electrical stimulation has widespread clinical and research applications, yet its effect on ongoing neural activity in humans is not well established. Previous reports argue that transcranial alternating current stimulation (tACS) can entrain and enhance neural rhythms related to memory, but the evidence from non-invasive recordings ha...