Layer-specific dynamics of local field potentials in monkey V1 during electrical stimulation.

The mammalian neocortex, organized into six cellular layers or laminae, forms a cortical network within layers. Layer specific computations are crucial for sensory processing of visual stimuli within primary visual cortex. Laminar recordings of local field potentials (LFPs) are a powerful tool to study neural activity within cortical layers.

Dissociation of Centrally and Peripherally Induced Transcranial Magnetic Stimulation Effects in Nonhuman Primates.

Transcranial magnetic stimulation (TMS) is a noninvasive brain stimulation method that is rapidly growing in popularity for studying causal brain-behavior relationships. However, its dose-dependent centrally induced neural mechanisms and peripherally induced sensory costimulation effects remain debated. Understanding how TMS stimulation parameters affect brain responses is vital for the rational design of TMS protocols.

Predicting the phase distribution during multi-channel transcranial alternating current stimulation in silico and in vivo.

Background: Transcranial alternating current stimulation (tACS) is a widely used noninvasive brain stimulation (NIBS) technique to affect neural activity. TACS experiments have been coupled with computational simulations to predict the electromagnetic fields within the brain. However, existing simulations are focused on the magnitude of the field.

Anatomical details affect electric field predictions for non-invasive brain stimulation in non-human primates.

Non-human primates (NHPs) have become key for translational research in noninvasive brain stimulation (NIBS). However, in order to create comparable stimulation conditions for humans it is vital to study the accuracy of current modeling practices across species. Numerical models to simulate electric fields are an important tool for experimental planning in NHPs and translation to human studies.

An open-access dataset of naturalistic viewing using simultaneous EEG-fMRI.

In this work, we present a dataset that combines functional magnetic imaging (fMRI) and electroencephalography (EEG) to use as a resource for understanding human brain function in these two imaging modalities. The dataset can also be used for optimizing preprocessing methods for simultaneously collected imaging data. The dataset includes simultaneously collected recordings from 22 individuals (ages: 23-51) across various visual and naturalistic stimuli.

Experimental validation of computational models for the prediction of phase distribution during multi-channel transcranial alternating current stimulation.

Transcranial alternating current stimulation (tACS) is a widely used noninvasive brain stimulation (NIBS) technique to affect neural activity. Neural oscillations exhibit phase-dependent associations with cognitive functions, and tools to manipulate local oscillatory phases can affect communication across remote brain regions. A recent study demonstrated that multi-channel tACS can generate electric fields with a phase gradient or traveling waves in the brain.

Dissociation of broadband high-frequency activity and neuronal firing in the neocortex.

Broadband high-frequency activity (BHA; 70 to 150 Hz), also known as "high gamma," a key analytic signal in human intracranial (electrocorticographic) recordings, is often assumed to reflect local neural firing [multiunit activity (MUA)]. As the precise physiological substrates of BHA are unknown, this assumption remains controversial. Our analysis of laminar multielectrode data from V1 and A1 in monkeys outlines two components of stimulus-evoked BHA distributed across the cortical layers: an "early-deep" and "late-superficial" response.

Electric field dynamics in the brain during multi-electrode transcranial electric stimulation.

Neural oscillations play a crucial role in communication between remote brain areas. Transcranial electric stimulation with alternating currents (TACS) can manipulate these brain oscillations in a non-invasive manner. Recently, TACS using multiple electrodes with phase shifted stimulation currents were developed to alter long-range connectivity.

Gradients of connectivity distance in the cerebral cortex of the macaque monkey.

Cortical connectivity conforms to a series of organizing principles that are common across species. Spatial proximity, similar cortical type, and similar connectional profile all constitute factors for determining the connectivity between cortical regions. We previously demonstrated another principle of connectivity that is closely related to the spatial layout of the cerebral cortex.

Top-down, contextual entrainment of neuronal oscillations in the auditory thalamocortical circuit.

Prior studies have shown that repetitive presentation of acoustic stimuli results in an alignment of ongoing neuronal oscillations to the sequence rhythm via oscillatory entrainment by external cues. Our study aimed to explore the neural correlates of the perceptual parsing and grouping of complex repeating auditory patterns that occur based solely on statistical regularities, or context. Human psychophysical studies suggest that the recognition of novel auditory patterns amid a continuous auditory stimulus sequence occurs automatically halfway through the first repetition.

Delineating the Macroscale Areal Organization of the Macaque Cortex In Vivo.

Complementing long-standing traditions centered on histology, fMRI approaches are rapidly maturing in delineating brain areal organization at the macroscale. The non-human primate (NHP) provides the opportunity to overcome critical barriers in translational research. Here, we establish the data requirements for achieving reproducible and internally valid parcellations in individuals.

Limitations of ex vivo measurements for in vivo neuroscience.

A long history of postmortem studies has provided significant insight into human brain structure and organization. Cadavers have also proven instrumental for the measurement of artifacts and nonneural effects in functional imaging, and more recently, the study of biophysical properties critical to brain stimulation. However, death produces significant changes in the biophysical properties of brain tissues, making an ex vivo to in vivo comparison complex, and even questionable.

Spatiotemporal structure of intracranial electric fields induced by transcranial electric stimulation in humans and nonhuman primates.

Transcranial electric stimulation (TES) is an emerging technique, developed to non-invasively modulate brain function. However, the spatiotemporal distribution of the intracranial electric fields induced by TES remains poorly understood. In particular, it is unclear how much current actually reaches the brain, and how it distributes across the brain.

Auditory properties in the parabelt regions of the superior temporal gyrus in the awake macaque monkey: an initial survey.

The superior temporal gyrus (STG) is on the inferior-lateral brain surface near the external ear. In macaques, 2/3 of the STG is occupied by an auditory cortical region, the "parabelt," which is part of a network of inferior temporal areas subserving communication and social cognition as well as object recognition and other functions. However, due to its location beneath the squamous temporal bone and temporalis muscle, the STG, like other inferior temporal regions, has been a challenging target for physiological studies in awake-behaving macaques.

Feedforward and feedback projections of caudal belt and parabelt areas of auditory cortex: refining the hierarchical model.

Our working model of the primate auditory cortex recognizes three major regions (core, belt, parabelt), subdivided into thirteen areas. The connections between areas are topographically ordered in a manner consistent with information flow along two major anatomical axes: core-belt-parabelt and caudal-rostral. Remarkably, most of the connections supporting this model were revealed using retrograde tracing techniques.

Anatomy of hierarchy: feedforward and feedback pathways in macaque visual cortex.

The laminar location of the cell bodies and terminals of interareal connections determines the hierarchical structural organization of the cortex and has been intensively studied. However, we still have only a rudimentary understanding of the connectional principles of feedforward (FF) and feedback (FB) pathways. Quantitative analysis of retrograde tracers was used to extend the notion that the laminar distribution of neurons interconnecting visual areas provides an index of hierarchical distance (percentage of supragranular labeled neurons [SLN]).

The spectrotemporal filter mechanism of auditory selective attention.

Although we have convincing evidence that attention to auditory stimuli modulates neuronal responses at or before the level of primary auditory cortex (A1), the underlying physiological mechanisms are unknown. We found that attending to rhythmic auditory streams resulted in the entrainment of ongoing oscillatory activity reflecting rhythmic excitability fluctuations in A1. Strikingly, although the rhythm of the entrained oscillations in A1 neuronal ensembles reflected the temporal structure of the attended stream, the phase depended on the attended frequency content.

A weighted and directed interareal connectivity matrix for macaque cerebral cortex.

Retrograde tracer injections in 29 of the 91 areas of the macaque cerebral cortex revealed 1,615 interareal pathways, a third of which have not previously been reported. A weight index (extrinsic fraction of labeled neurons [FLNe]) was determined for each area-to-area pathway. Newly found projections were weaker on average compared with the known projections; nevertheless, the 2 sets of pathways had extensively overlapping weight distributions.

Dual mechanism of neuronal ensemble inhibition in primary auditory cortex.

Inhibition plays an essential role in shaping and refining the brain's representation of sensory stimulus attributes. In primary auditory cortex (A1), so-called "sideband" inhibition helps to sharpen the tuning of local neuronal responses. Several distinct types of anatomical circuitry could underlie sideband inhibition, including direct thalamocortical (TC) afferents, as well as indirect intracortical mechanisms.

Weight consistency specifies regularities of macaque cortical networks.

To what extent cortical pathways show significant weight differences and whether these differences are consistent across animals (thereby comprising robust connectivity profiles) is an important and unresolved neuroanatomical issue. Here we report a quantitative retrograde tracer analysis in the cynomolgus macaque monkey of the weight consistency of the afferents of cortical areas across brains via calculation of a weight index (fraction of labeled neurons, FLN). Injection in 8 cortical areas (3 occipital plus 5 in the other lobes) revealed a consistent pattern: small subcortical input (1.

Projection from visual areas V2 and prostriata to caudal auditory cortex in the monkey.

Studies in humans and monkeys report widespread multisensory interactions at or near primary visual and auditory areas of neocortex. The range and scale of these effects has prompted increased interest in interconnectivity between the putatively "unisensory" cortices at lower hierarchical levels. Recent anatomical tract-tracing studies have revealed direct projections from auditory cortex to primary visual area (V1) and secondary visual area (V2) that could serve as a substrate for auditory influences over low-level visual processing.

Multisensory connections of monkey auditory cerebral cortex.

Functional studies have demonstrated multisensory responses in auditory cortex, even in the primary and early auditory association areas. The features of somatosensory and visual responses in auditory cortex suggest that they are involved in multiple processes including spatial, temporal and object-related perception. Tract tracing studies in monkeys have demonstrated several potential sources of somatosensory and visual inputs to auditory cortex.

Long-distance feedback projections to area V1: implications for multisensory integration, spatial awareness, and visual consciousness.

It is generally agreed that information flow through the cortex is constrained by a hierarchical architecture. Recent experimental evidence suggests that projections descending the hierarchy and targeting the primary visual cortex (area V1) may play an essential role in perceptual processes. We have, therefore, reexamined feedback projections to area V1, using retrograde tracer injections in this area In addition to well-known areas, quantification of labeling in higher cortical areas reveals a number of hitherto unknown long-distance feedback connections originating from auditory (A1), multisensory (STP) cortices, but also from a perirhinal area (36).