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Cognitive deficits are a common consequence of traumatic brain injury. Although such deficits are amenable to rehabilitation, methods for individualizing cognitive interventions are still unrefined. Functional neuroimaging methods such as positron emission tomography and functional magnetic resonance imaging are emerging as possible technologies for measuring and monitoring the cerebral consequences of plasticity associated with brain injury and for evaluating the effectiveness of rehabilitation interventions. Functional neuroimaging may even enable more customized and efficient selection, design, or adaptation of individual cognitive rehabilitation programs. We review the current literature on functional neuroimaging after traumatic brain injury, relating these findings to cognitive rehabilitation. Overall, functional neuroimaging after traumatic brain injury has shown reliable differences in brain activity within several regions of frontal cortex, partly but not uniformly consistent with neuropsychological and structural findings in traumatic brain injury. We also outline a number of promising research opportunities for applying functional neuroimaging in traumatic brain injury settings, along with associated challenges. [ABSTRACT FROM AUTHOR]

OBJECTIVES: To review the use of near-infrared spectroscopy (NIRS) in stroke rehabilitation and to evaluate NIRS test-retest reliability within-session on a motor control task commonly used in neuroimaging of stroke recovery. DESIGN: Cohort study. SETTING: Hospital-based research laboratory. PARTICIPANTS: Nineteen healthy control subjects (age range, 22-55y). INTERVENTIONS: Subjects performed 2 experimental runs of a finger-opposition task in a block-design paradigm (finger opposition alternated with a fixation rest period) while undergoing multichannel NIRS and physiologic monitoring. MAIN OUTCOME MEASURE: Reliability coefficients (Pearson r) for oxyhemoglobin (O(2)Hb) and deoxyhemoglobin (HHb) correlated amplitude modulations across measurement channels during individual blocks and block averages. RESULTS: Correlations between single blocks (ie, 16-s slices of data) exhibited a correlation intercept of .33+/-.09 for O(2)Hb. This value was minimally decreased by increasing lag between compared blocks (slope, -.012; P=.019) but was substantially enhanced by averaging across blocks (within-run slope, .11; between-run slope, .044). Correlations using 64 seconds of data reached 0.6. Results for HHb were virtually identical. CONCLUSIONS: NIRS modulations were repeatable even when comparing very short segments of data. When averaging longer data segments, the test-retest correspondences compared favorably to neuroimaging using other modalities. This suggests that NIRS is a reliable tool for longitudinal stroke rehabilitation and recovery studies. Copyright © 2006 by the American Congress of Rehabilitation Medicine and the American Academy of Physical Medicine and Rehabilitation [ABSTRACT FROM AUTHOR]

Objectives: To evaluate if the tackler correctly adhering, or not, to four different instructions of legal front-on one-on-one torso tackles altered the tackler and/or ball carrier peak inertial head kinematics., Design: Controlled laboratory study., Methods: Fifteen rugby-code players measured with three-dimensional optoelectronic motion capture performed two tackle instructions from the Australian National Rugby League coaching manual on under (Dominant National Rugby League) and over (Smother National Rugby League) the ball tackles, and two novel variants of these (under, Dominant, Torso Stick; over, Smother, Pop, Lock). A series of mixed general linear models identified if the tackler adhering (n = 455), or not (n = 139) to the tackle instructions altered peak inertial head kinematics., Results: The tackler's peak inertial head kinematics did not significantly change whether or not they adhered to each of the tackle instructions. When the tackler did adhere to the instructions, the ball carrier sustained a lower peak inertial head kinematics (p < 0.01) in the Smother National Rugby League tackle but higher peak inertial head kinematics in the Smother, Pop, Lock., Conclusions: The ball carriers' inertial head kinematics but not the tacklers were increased when the tackler adhered to this study's variants of the over and under the ball tackle instructions, suggesting that the tacklers were more effective in their tackle performance than the traditional tackle instructions when adhering to the tackle instruction. Greater adherence to the under the ball instructions suggests that the over the ball instruction is a more challenging technique to learn., Competing Interests: Declaration of interest statement Suzi Edwards declares that they have no conflict of interest. Andrew Gardner, Ph.D. has a clinical practice in neuropsychology involving individuals who have sustained sport-related concussion (including current and former athletes). He has been a contracted concussion consultant to Rugby Australia (2016–). He has received travel funding or been reimbursed by professional sporting bodies, and commercial organisations for discussing or presenting sport-related concussion research at meetings, scientific conferences, workshops, and symposiums. He has received research funding from the National Rugby League (NRL) for the Retired Players Brain Health research programme. Previous grant funding includes the NSW Sporting Injuries Committee, the Brain Foundation (Australia), an Australian–American Fulbright Commission Postdoctoral Award, a Hunter New England Local Health District, Research, Innovation and Partnerships Health Research & Translation Centre and Clinical Research Fellowship Scheme, and the Hunter Medical Research Institute (HMRI), supported by Jennie Thomas, and the HMRI, supported by Anne Greaves. He has served as a scientific advisor for hitIQ Ltd. Ross Tucker is a research consultant to World Rugby (Pty) Ltd, the governing body for Rugby Union globally. Ken Quarrie is employed as the senior sport scientist for New Zealand Rugby. Grant Iverson serves as a scientific advisor for NanoDx™ (formerly BioDirection, Inc.), Sway Operations, LLC, and Highmark, Inc. He has a clinical and consulting practice in forensic neuropsychology, including expert testimony, involving individuals who have sustained mild TBIs (including athletes). He has received research funding from several test publishing companies, including ImPACT Applications, Inc., CNS Vital Signs, and Psychological Assessment Resources (PAR, Inc.). He has received research funding as a principal investigator from the National Football League, and salary support as a collaborator from the Harvard Integrated Program to Protect and Improve the Health of National Football League Players Association Members. Gary Strangman has received pilot research funding from the Harvard Football Player's Health Study, funded through the National Football League Players Association., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Long-duration spaceflight is associated with pathophysiological changes in the intracranial compartment hypothetically linked to microgravity-induced headward fluid shift. This study aimed to determine whether daily artificial gravity (AG) sessions can mitigate these effects, supporting its application as a countermeasure to spaceflight. Twenty-four healthy adult volunteers (16 men) were exposed to 60 days of 6° head-down tilt bed rest (HDTBR) as a ground-based analog of chronic headward fluid shift. Subjects were divided equally into three groups: no AG (control), daily 30-min intermittent AG (iAG), and daily 30-min continuous (cAG). Internal carotid artery (ICA) stroke volume (ICA SV ), ICA resistive index (ICA RI ), ICA flow rate (ICA FR ), aqueductal cerebral spinal fluid flow velocity (CSF V ), and intracranial volumetrics were quantified at 3 T. MRI was performed at baseline, 14 and 52 days into HDTBR, and 3 days after HDTBR (recovery). A mixed model approach was used with intervention and time as the fixed effect factors and the subject as the random effect factor. Compared with baseline, HDTBR was characterized by expansion of lateral ventricular, white matter, gray matter, and brain + total intracranial cerebral spinal fluid volumes, increased CSFv, decreased ICA SV , and decreased ICA FR by 52 days into HBTBR (All P s < 0.05). ICA RI was only increased 14 days into HDTBR ( P < 0.05). Neither iAG nor cAG significantly affected measurements compared with HDTBR alone, indicating that 30 min of daily exposure was insufficient to mitigate the intracranial effects of headward fluid shift. Greater AG session exposure time, gravitational force, or both are suggested for future countermeasure research. NEW & NOTEWORTHY Brief exposure to continuous or intermittent artificial gravity via short-arm centrifugation was insufficient in mitigating the intracranial pathophysiological effects of the headward fluid shift simulated during head-down tilt bed rest (HDTBR). Our results suggest that greater centrifugation session duration, gravitational force, or both may be required to prevent the development of spaceflight-associated neuro-ocular syndrome and should be considered in future ground-based countermeasure studies.

Objective: This paper surveys the existing literature surrounding problem-solving and team dynamics in complex and unpredictable scenarios, and evaluates the applicability of studying Earth-based construction teams to identify training needs for Lunar construction crews., Background: Lunar and other space exploration construction crews will work in extreme environments and face unpredictable challenges, necessitating real-time problem-solving to address unexpected contingencies. This work will require coordination with Mission Control and autonomous assistants, so crew training must account for multi-agent, distributed teamwork., Method: A narrative literature review identified processes, attributes, and skills necessary for the success of Lunar construction teams. We summarized relevant frameworks and synthesized collective findings into over-arching trends and remaining research gaps., Results: While significant literature exists surrounding team performance, very little systematic inquiry has been done with a focus on Lunar construction crews and operations, particularly with respect to dynamic problem-solving and team-based decision-making. Established and standardized metrics for evaluating team performance are lacking, resulting in significant variation in reported outcomes between studies., Conclusion: Lunar and other space exploration construction teams will need training that focuses on developing the right approach to team-based problem-solving, rather than on preparing response execution for known contingencies. An investigation of successful Earth-based construction crews may facilitate the development of relevant metrics for training future Lunar construction crews., Application: Metrics and team training protocols developed for future Lunar construction teams may be adaptable and applicable to a wide range of extreme teams facing uncertain challenges, such as aircrews, surgical teams, first responders, and construction crews.

Aerospace research has a long history of developing technologies with industry-changing applications and recent history is no exception. The expansion of commercial spaceflight and the upcoming exploration-class missions to the Moon and Mars are expected to accelerate this process even more. The resulting portable, wearable, contactless, and regenerable medical technologies are not only the future of healthcare in deep space but also the future of healthcare here on Earth. These multi-dimensional and integrative technologies are non-invasive, easily-deployable, low-footprint devices that have the ability to facilitate rapid detection, diagnosis, monitoring, and treatment of a variety of conditions, and to provide decision-making and performance support. Therefore, they are primed for applications in low-resource and remote environments, facilitating the extension of quality care delivery to all patients in all communities and empowering non-specialists to intervene early and safely in order to optimize patient-centered outcomes. Additionally, these technologies have the potential to advance care delivery in tertiary care centers by improving transitions of care, providing holistic patient data, and supporting clinician wellness and performance. The requirements of space exploration have created a number of paradigm-altering medical technologies that are primed to revitalize and elevate our standard of care here on Earth., Competing Interests: SP is employed by company Fluidity Technologies, Inc. SP is employed by Operator Solutions and Voyager Space Holdings as a board member. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Scarpa, Parazynski and Strangman.)

Spaceflight associated neuro-ocular syndrome (SANS) refers to a unique collection of neuro-ophthalmic clinical and imaging findings observed in astronauts after long-duration spaceflight. Current in-flight and postflight imaging modalities (e.g., optical coherence tomography, orbital ultrasound, and funduscopy) have played an instrumental role in the understanding and monitoring of SANS development; however, the precise etiology for this neuro-ophthalmic phenomenon is still not completely understood. SANS may be a potential barrier to future deep space missions, and therefore it is critical to further elucidate the underlying pathophysiology for effective countermeasures. The complexity and unique limitations of spaceflight require careful consideration and integration of leading technology to advance our knowledge of this extraterrestrial syndrome. We describe the current neuro-ophthalmic imaging modalities and hypotheses that have improved our current understanding of SANS, discuss newer developments in SANS imaging (including noninvasive near-infrared spectroscopy) and summarize emerging research in the development of an aspirational future head-mounted virtual reality display with multimodal visual assessment technology for the detection of neuro-ocular findings in SANS., Competing Interests: Conflict of interest The authors AT & GS have received grants from the National Aeronautics and Space Administration (Grants 80NSSC20K1831 and NCC958SMST02801, respectively) to conduct and develop the research detailed in this manuscript. Apart from this funding, the authors report no commercial or proprietary interest in the products or concepts discussed in this article., (Copyright © 2022. Published by Elsevier Inc.)

Purpose: This study aimed to investigate how four types of successfully executed, legal front-on, one-on-one torso tackles influence the tacklers' and ball carriers' inertial head kinematics., Methods: A total of 455 successful front-on, one-on-one torso tackle trials completed by 15 rugby code players using three-dimensional motion capture were recorded. Tackles differed with respects to the height of the contact point on the ball carrier's torso. A series of mixed general linear models were conducted., Results: The tackler sustained the highest peak resultant linear ( P < 0.001) and angular ( P < 0.01) head accelerations when contacting the lower torso to execute a "dominant" tackle compared with mid or upper torso, although these latter tackle types had the lowest ball carrier inertial head kinematics. When executing a "smother" tackle technique, a significant decrease in peak resultant linear head acceleration was observed with a vertical "pop" then lock action used, compared with the traditional upper torso tackling technique ( P < 0.001)., Conclusions: Modifying the tackler's engagement with a ball carrier's torso, with respect to height and technical execution, alters the inertial head kinematics of the tackler and the ball carrier. The traditional thinking about optimal tackle technique, as instructed, may need to be reevaluated, with the midtorso being a potential alternative target contact height, whereas changes in tackle execution may be relatively protective for tacklers when executing either a dominant or smother tackle. This study provides critical scientific evidence to underpin revised coaching tackling technique interventions that might enhance player safety. Tackles in which the tackler contacts the ball carrier around the midtorso region, rather than lower torso, produce the lowest acceleration and thus may contribute to reducing head injury risk for the tackler., (Copyright © 2022 The Author(s). Published by Wolters Kluwer Health, Inc. on behalf of the American College of Sports Medicine.)

In this paper, we investigate the potential of generic physiological features of stress resilience in predicting air traffic control (ATC) candidates' performance in a highly-stressful low-fidelity ATC simulator scenario. Stress resilience is highlighted as an important occupational factor that influences the performance and well-being of air traffic control officers (ATCO). Poor stress management, besides the lack of skills, can be a direct cause of poor performance under stress, both in the selection process of ATCOs and later in the workplace. 40 ATC candidates, within the final stages of their selection process, underwent a stimulation paradigm for elicitation and assessment of various generic task-unrelated physiological features, related to resting heart rate variability (HRV) and respiratory sinus arrhythmia (RSA), acoustic startle response (ASR) and the physiological allostatic response, which are all recognized as relevant psychophysiological markers of stress resilience. The multimodal approach included analysis of electrocardiography, electromyography, electrodermal activity and respiration. We make advances in computational methodology for assessment of physiological features of stress resilience, and investigate the predictive power of the obtained feature space in a binary classification problem: prediction of high- vs. low-performance on the developed ATC simulator. Our novel approach yields a relatively high 78.16% classification accuracy. These results are discussed in the context of prior work, while considering study limitations and proposing directions for future work.

Exploration of deep space poses many challenges. Mission support personnel will not be immediately available to assist crewmembers performing complex operations on future long-duration exploration operations. Consequently, it is imperative that crewmembers have objective, reliable, and non-invasive metrics available to aid them in determining their fitness for duty prior to engaging in potentially dangerous tasks. The Robotics On-Board Trainer (ROBoT) task is NASA's platform for training astronauts to perform docking and grappling maneuvers. It is regularly used by crewmembers during spaceflight for refresher training. The operational ROBoT system, however, does not record data. Thus, a research version of ROBoT, called ROBoT-r, was developed so that operationally relevant data could be mined to provide feedback to crewmembers. We investigated whether ROBoT-r metrics would change according to sleep loss and circadian phase in a 28-h laboratory-based sleep deprivation study. Overall, participants showed improvement over time despite sleep loss, indicating continued learning. Performance on the psychomotor vigilance task (PVT) followed an expected profile, with reduced performance across the night. These findings suggest that individuals may be able to temporarily compensate for sleep loss to maintain performance on complex, novel tasks. It is possible that some ROBoT-r metrics may be sensitive to sleep loss after longer bouts of wakefulness or after individuals have habituated to the task. Studies with additional participants and extended pre-training on the ROBoT-r task should be conducted to disentangle how brain activity may change as individuals learn and habituate to complex tasks during sleep loss., (Copyright © 2020 Wong, Pradhan, Karasinski, Hu, Strangman, Ivkovic, Arsintescu and Flynn-Evans.)

Exposure to the microgravity environment results in various adaptive and maladaptive physiological changes in the human body, with notable ophthalmic abnormalities developing during 6-mo missions on the International Space Station (ISS). These findings have led to the hypothesis that the loss of gravity induces a cephalad fluid shift, decreased cerebral venous outflow, and increased intracranial pressure, which may be further exacerbated by increased ambient carbon dioxide (CO 2 ) levels on the ISS. Here we describe the SPACECOT study (studying the physiological and anatomical cerebral effects of CO 2 during head-down tilt), a randomized, double-blind crossover design study with two conditions: 29 h of 12° head-down tilt (HDT) with ambient air and 29 h of 12° HDT with 0.5% CO 2 The internationally collaborative SPACECOT study utilized an innovative approach to study the effects of headward fluid shifting induced by 12° HDT and increased ambient CO 2 as well as their interaction with a focus on cerebral and ocular anatomy and physiology. Here we provide an in-depth overview of this new approach including the subjects, study design, and implementation, as well as the standardization plan for nutritional intake, environmental parameters, and bed rest procedures. NEW & NOTEWORTHY A new approach for investigating the combined effects of cephalad fluid shifting and increased ambient carbon dioxide (CO 2 ) is presented. This may be useful for studying the neuroophthalmic and cerebral effects of spaceflight where cephalad fluid shifts occur in an elevated CO 2 environment., (Copyright © 2017 the American Physiological Society.)

Several neuroimaging studies have demonstrated compensatory cerebral responses consequent to sleep deprivation (SD), but all have focused on simple tasks with limited behavioral response options. We assessed the cerebral effects associated with SD during the performance of a complex, open-ended, dual-joystick, 3D navigation task (simulated orbital docking) in a cross-over protocol, with counterbalanced orders of normal sleep (NS) and a single night of total SD (approximately 27 h). Behavioral performance on multiple measures was comparable in the two sleep conditions. Functional magnetic resonance imaging revealed multiple compensatory SD > NS cerebral responses, including the posterior superior temporal sulcus [Brodmann area (BA) 39/22/37], prefrontal cortex (BA 9), lateral temporal cortex (BA 22/21), and right substantia nigra. Right posterior cingulate cortex (BA 31) exhibited NS > SD activity. Our findings extend the compensatory cerebral response hypothesis to complex, open-ended tasks.

Objective: To investigate the behavioral and neural effects of rule-based knowledge on motor sequence learning., Methods: The authors developed a novel 2-dimensional variant of the serial reaction time (SRT) task to test the effect of prior, verbalizable rule knowledge on motor learning behavior. To examine neurophysiological effects, they also performed functional magnetic resonance imaging on a small cohort of subjects while performing the same task., Results: Behavioral data demonstrated that instruction on sequence-governing rules enhanced behavioral performance in both learning magnitudes and rates. The neuroimaging data revealed substantially different, but partially overlapping, learning-related activation patterns with and without prior rule instruction. Direct comparison of these 2 conditions revealed significantly different involvement of bilateral superior and anterior prefrontal cortex (Brodmann areas 8 and 10, respectively), right superior temporal cortex (BA 38/21), and left cerebellum., Conclusions: These behavioral findings demonstrate an advantage of teaching governing rules prior to 2D-SRT task performance. While these neuroimaging findings remain to be replicated in a larger cohort of subjects, results suggest that substantially different-though partially overlapping-brain regions subserve learning in these 2 rehabilitation-relevant conditions. Thus, appropriate choice of pretraining may benefit, for example, rehabilitation populations, at least in motor skill acquisition that requires sequencing.

Near-infrared spectroscopy (NIRS) can be used to noninvasively measure changes in the concentrations of oxy- and deoxyhemoglobin in tissue. We have previously shown that while global changes can be reliably measured, focal changes can produce erroneous estimates of concentration changes (NeuroImage 13 (2001), 76). Here, we describe four separate sources for systematic error in the calculation of focal hemoglobin changes from NIRS data and use experimental methods and Monte Carlo simulations to examine the importance and mitigation methods of each. The sources of error are: (1). the absolute magnitudes and relative differences in pathlength factors as a function of wavelength, (2). the location and spatial extent of the absorption change with respect to the optical probe, (3). possible differences in the spatial distribution of hemoglobin species, and (4). the potential for simultaneous monitoring of multiple regions of activation. We found wavelength selection and optode placement to be important variables in minimizing such errors, and our findings indicate that appropriate experimental procedures could reduce each of these errors to a small fraction (<10%) of the observed concentration changes.

Near-infrared spectroscopy (NIRS) has been used to noninvasively monitor adult human brain function in a wide variety of tasks. While rough spatial correspondences with maps generated from functional magnetic resonance imaging (fMRI) have been found in such experiments, the amplitude correspondences between the two recording modalities have not been fully characterized. To do so, we simultaneously acquired NIRS and blood-oxygenation level-dependent (BOLD) fMRI data and compared Delta(1/BOLD) (approximately R(2)(*)) to changes in oxyhemoglobin, deoxyhemoglobin, and total hemoglobin concentrations derived from the NIRS data from subjects performing a simple motor task. We expected the correlation with deoxyhemoglobin to be strongest, due to the causal relation between changes in deoxyhemoglobin concentrations and BOLD signal. Instead we found highly variable correlations, suggesting the need to account for individual subject differences in our NIRS calculations. We argue that the variability resulted from systematic errors associated with each of the signals, including: (1) partial volume errors due to focal concentration changes, (2) wavelength dependence of this partial volume effect, (3) tissue model errors, and (4) possible spatial incongruence between oxy- and deoxyhemoglobin concentration changes. After such effects were accounted for, strong correlations were found between fMRI changes and all optical measures, with oxyhemoglobin providing the strongest correlation. Importantly, this finding held even when including scalp, skull, and inactive brain tissue in the average BOLD signal. This may reflect, at least in part, the superior contrast-to-noise ratio for oxyhemoglobin relative to deoxyhemoglobin (from optical measurements), rather than physiology related to BOLD signal interpretation.

This article reviews diffuse optical brain imaging, a technique that employs near-infrared light to non-invasively probe the brain for changes in parameters relating to brain function. We describe the general methodology, including types of measurements and instrumentation (including the tradeoffs inherent in the various instrument components), and the basic theory required to interpret the recorded data. A brief review of diffuse optical applications is included, with an emphasis on research that has been done with psychiatric populations. Finally, we discuss some practical issues and limitations that are relevant when conducting diffuse optical experiments. We find that, while diffuse optics can provide substantial advantages to the psychiatric researcher relative to the alternative brain imaging methods, the method remains substantially underutilized in this field.

Near infrared spectroscopy (NIRS) can detect changes in the concentrations of oxy-hemoglobin ([HbO]) and deoxy-hemoglobin ([Hb]) in tissue based upon differential absorption at multiple wavelengths. The common analysis of NIRS data uses the modified Beer-Lambert law, which is an empirical formulation that assumes global concentration changes. We used simulations to examine the errors that result when this analysis is applied to focal hemodynamic changes, and we performed simultaneous NIRS measurements during a motor task in adult humans and a neonate to evaluate the dependence of the measured changes on detector-probe geometry. For both simulations and in vivo measurements, the wide range of NIRS results was compared to an imaging analysis, diffuse optical tomography (DOT). The results demonstrate that relative changes in [HbO] and [Hb] cannot, in general, be quantified with NIRS. In contrast to that method, DOT analysis was shown to accurately quantify simulated changes in chromophore concentrations. These results and the general principles suggest that DOT can accurately measure changes in [Hb] and [HbO], but NIRS cannot accurately determine even relative focal changes in these chromophore concentrations. For the standard NIRS analysis to become more accurate for focal changes, it must account for the position of the focal change relative to the source and detector as well as the wavelength dependent optical properties of the medium., (Copyright 2001 Academic Press.)

Two statistical methods-cross-correlation (Moore et al. 1966) and gravity clustering (Gerstein et al. 1985)-were evaluated for their ability to detect synchronous cell assemblies from simulated spike train data. The two methods were first analyzed for their temporal sensitivity to synchronous cell assemblies. The presented approach places a lower bound on the amount of data required to detect a synchronous assembly. On average, both methods required the same minimum amount of recording time to detect significant pairwise correlations, but the gravity method exhibited less variance in the recording time. The precise length of recording depends on the consistency with which a neuron fires synchronously with the assembly but was independent of the assembly firing rate. Next, the statistical methods were tested with respect to their ability to differentiate two distinct assemblies that overlapped in time and space. Both statistics could adequately differentiate two overlapping synchronous assemblies. For cross-correlation, this ability deteriorates quickly when considering three or more simultaneously active, overlapping assemblies, whereas the gravity method should be more flexible in this regard. The work demonstrates the difficulty of detecting assembly phenomena from simultaneous neuronal recordings. Other statistical methods and the detection of other types of assemblies are also discussed.

Two methods were derived to estimate the probability of recording cell assemblies using multiple simultaneous electrode recordings. The derivations are independent of the definition of a cell assembly, and require only a statistic for evaluating cell assembly membership from spike train data. The resulting equations are functions of 1) the size of the search area, 2) the smallest expected assembly size, 3) the number of recorded neurons, and 4) the predicted spatial distribution of assembly neurons. The equations can be used to estimate the following three quantities. First, the equations directly calculate the probability of detecting i or more cells of an hypothesized assembly. Second, by making several such calculations, one can estimate when sufficient sampling has been performed to claim, at any desired confidence level, that a posited type of cell assembly does not exist. Third, the probability of detecting one out of several active assemblies can be calculated, given assumptions about assembly-assembly interactions.