Spatial patterns of spontaneous neural activity at rest have previously been associated with specific networks in the brain, including those pertaining to the functional architecture of the primary visual cortex (V1). However, despite the prominent anatomical differences between cortical layers, little is known about the laminar pattern of spontaneous activity in V1. We address this topic by investigating the amplitude and coherence of ongoing local field potential (LFP) signals measured from different layers in V1 of macaque monkeys during rest and upon presentation of a visual stimulus. We used a linear microelectrode array to measure LFP signals at multiple, evenly spaced positions throughout the cortical thickness. Analyzing both the mean LFP amplitudes and between-contact LFP coherences, we identified two distinct zones of activity, roughly corresponding to superficial and deep layers, divided by a sharp transition near the bottom of layer 4. The LFP signals within each laminar zone were highly coherent, whereas those between zones were not. This functional compartmentalization was found not only during rest, but also when the receptive field was stimulated during a visual task. These results demonstrate the existence of distinct superficial and deep functional domains of coherent LFP activity in V1 that may reflect the intrinsic interplay of V1 microcircuitry with cortical and subcortical targets, respectively.

The role of primary visual cortex (V1) in determining the contents of perception is controversial. Human functional imaging (fMRI) studies of perceptual suppression have revealed a robust drop in V1 activity when a stimulus is subjectively invisible. In contrast, monkey single unit recordings have failed to demonstrate such perception locked changes in V1. To investigate the basis of this discrepancy, we measured both the blood oxygenation level-dependent (BOLD) response and several electrophysiological signals in two behaving monkeys. We found that during conventional stimulus presentation, all signals were in good agreement, showing strong visual modulation to presentation and removal of a stimulus. However, during perceptual suppression, only the BOLD response and low frequency local field potential (LFP) signals exhibited decreases, while the spiking and high frequency LFP signals were unaffected. These results demonstrate that the coupling between the BOLD and electrophysiological signals in V1 is context dependent, with a marked dissociation occurring during perceptual suppression.

A local field potential (LFP) response can be measured throughout the visual cortex in response to the abrupt appearance of a visual stimulus. Averaging LFP responses to many stimulus presentations isolates transient, phase-locked components of the response that are consistent from trial to trial. However, stimulus responses are also composed of sustained components, which differ in their phase from trial to trial and therefore must be evaluated using other methods, such as computing the power of the response of each trial before averaging. Here, we investigate the basis of phase-locked and non-phase-locked LFP responses in the primary visual cortex of the macaque monkey using a novel variant of current source density (CSD) analysis. We applied a linear array of electrode contacts spanning the thickness of the cortex to measure the LFP and compute band-limited CSD power to identify the laminar sites of persistent current exchange that may be the basis of sustained visual LFP responses. In agreement with previous studies, we found a short-latency phaselocked current sink, thought to correspond to thalamocortical input to layer 4C. In addition, we found a prominent non-phase-locked component of the CSD that persisted as long as the stimulus was physically present. The latter was relatively broadband, lasted throughout the stimulus presentation, and was centered ϳ500 m deeper than the initial current sink. These findings demonstrate a fundamental difference in the neural mechanisms underlying the initial and sustained processing of simple visual stimuli in the V1 microcircuit.

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This study is a part of an ongoing series of studies examining cueing modalities to circumvent the in-flight effects of degraded visual environments (DVEs) in a rotary wing aircraft. The suite of cueing modalities investigated include visual cueing symbology, auditory cueing, and tactile cueing. This study compared the use of combinations of these cueing modalities to find which resulted in the best performance and the least amount of workload required of the pilot. This specific paper focuses on the analysis of pupillometric data collected through video-based eye-tracking to measure cognitive workload. Results are discussed.

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82.3% of the traumatic brain injuries that U.S. Service Members and civilians sustain are concussions, also termed mild traumatic brain injuries (mTBI). Although the effects of concussion are relatively easy to diagnose in the acute phase, diagnosis remains difficult during the chronic phase. Here, we present data demonstrating improved sensitivity to oculomotor deficits of chronic mTBI through the use of a normorbaric hypoxic stress paradigm that approximates the partial pressure of oxygen encountered at about 13,000 feet above mean sea level. Saccadic performance was compared between mTBI and healthy control groups across normoxia, hypoxia, and finally upon return to normoxia. When compared to healthy controls at initial normoxia, the mTBI group showed a trend to poorer performance. At hypoxia and on return-to-normoxia, the difference between the groups increased to become statistically significant. Thus, hypoxia resulted in an increased saccadic impairment in the mTBI group, and, perhaps more importantly, the mTBI group evidenced a delayed recovery upon return to normoxia.