pyElectrode: an open-source tool using structural MRI for electrode positioning and neuron mapping

Dorsal raphe neurons integrate the values of reward amount, delay, and uncertainty in multi-attribute decision-making

The dorsal raphe nucleus (DRN) is implicated in psychiatric disorders that feature impaired sensitivity to reward amount, impulsivity when facing reward delays, and risk-seeking when confronting reward uncertainty. However, it has been unclear whether and how DRN neurons signal reward amount, reward delay, and reward uncertainty during multi-attribute value-based decision-making, where subjects consider these attributes to make a choice. We recorded DRN neurons as monkeys chose between offers whose attributes, namely expected reward amount, reward delay, and reward uncertainty, varied independently. Many DRN neurons signaled offer attributes, and this population tended to integrate the attributes in a manner that reflected monkeys' preferences for amount, delay, and uncertainty. After decision-making, in response to post-decision feedback, these same neurons signaled signed reward prediction errors, suggesting a broader role in tracking value across task epochs and behavioral contexts. Our data illustrate how the DRN participates in value computations, guiding theories about the role of the DRN in decision-making and psychiatric disease.

A neural mechanism for conserved value computations integrating information and rewards

Behavioral and economic theory dictate that we decide between options based on their values. However, humans and animals eagerly seek information about uncertain future rewards, even when this does not provide any objective value. This implies that decisions are made by endowing information with subjective value and integrating it with the value of extrinsic rewards, but the mechanism is unknown. Here, we show that human and monkey value judgements obey strikingly conserved computational principles during multi-attribute decisions trading off information and extrinsic reward. We then identify a neural substrate in a highly conserved ancient structure, the lateral habenula (LHb). LHb neurons signal subjective value, integrating information's value with extrinsic rewards, and the LHb predicts and causally influences ongoing decisions. Neurons in key input areas to the LHb largely signal components of these computations, not integrated value signals. Thus, our data uncover neural mechanisms of conserved computations underlying decisions to seek information about the future.

Dorsal raphe neurons signal integrated value during multi-attribute decision-making

The dorsal raphe nucleus (DRN) is implicated in psychiatric disorders that feature impaired sensitivity to reward amount, impulsivity when facing reward delays, and risk-seeking when grappling with reward uncertainty. However, whether and how DRN neurons signal reward amount, reward delay, and reward uncertainty during multi-attribute value-based decision-making, where subjects consider all these attributes to make a choice, is unclear. We recorded DRN neurons as monkeys chose between offers whose attributes, namely expected reward amount, reward delay, and reward uncertainty, varied independently. Many DRN neurons signaled offer attributes. Remarkably, these neurons commonly integrated offer attributes in a manner that reflected monkeys' overall preferences for amount, delay, and uncertainty. After decision-making, in response to post-decision feedback, these same neurons signaled signed reward prediction errors, suggesting a broader role in tracking value across task epochs and behavioral contexts. Our data illustrate how DRN participates in integrated value computations, guiding theories of DRN in decision-making and psychiatric disease.

A multimodal imaging-guided software for access to primate brains

Background

Imaging-guided access to the brain has become a routine procedure for various research and clinical applications, including drug administration, neurophysiological recording, and sampling tissue. Therefore, open-source software is required to handle such datasets in these specific applications.

New methods

Here, we proposed an open-source tool utilizing different imaging modalities for automating the steps to access the brain. This tool provides means for easily calculating the coordination of the area of interest concerning a specific point of entry. The source and documentation are available at this link.

Results

We have used this software for three different applications: electrophysiological recording, drug infusion in the nonhuman primate brain, and guided biopsy procedure in the human brain. We performed a neural recording of two monkeys' prefrontal cortex and inferior temporal cortex using this software in submillimeter resolution. We also applied our procedure for infusion in the putamen and caudate nuclei in both hemispheres of another group of rhesus monkeys with histological proof in one animal. More so, we validated this software in the human subjects that underwent biopsy surgery with the commercial software used in human biopsy surgery.

Comparison with existing methods

Our software uses different imaging modalities by co-registering them. This will provide structural details of the skull and brain tissue. We can calculate each brain region's coordination at the point of entry by re-slicing the images. Atlas-based image segmentation were implemented in our software. Three mentioned applications of our software in neuroscience will be further discussed in this paper.

Conclusion

In our procedure, working with different imaging modalities provides a precise estimation of the specific region in the brain related to the location of implants or stereotaxic frames. There is no limitation to using metal implants in this procedure.

Laser stimulation of the skin for quantitative study of decision-making and motivation

Neuroeconomics studies how decision-making is guided by the value of rewards and punishments. But to date, little is known about how noxious experiences impact decisions. A challenge is the lack of an aversive stimulus that is dynamically adjustable in intensity and location, readily usable over many trials in a single experimental session, and compatible with multiple ways to measure neuronal activity. We show that skin laser stimulation used in human studies of aversion can be used for this purpose in several key animal models. We then use laser stimulation to study how neurons in the orbitofrontal cortex (OFC), an area whose many roles include guiding decisions among different rewards, encode the value of rewards and punishments. We show that some OFC neurons integrated the positive value of rewards with the negative value of aversive laser stimulation, suggesting that the OFC can play a role in more complex choices than previously appreciated.

A primate temporal cortex-zona incerta pathway for novelty seeking

Primates interact with the world by exploring visual objects; they seek opportunities to view novel objects even when these have no extrinsic reward value. How the brain controls this novelty seeking is unknown. Here we show that novelty seeking in monkeys is regulated by the zona incerta (ZI). As monkeys made eye movements to familiar objects to trigger an opportunity to view novel objects, many ZI neurons were preferentially activated by predictions of novel objects before the gaze shift. Low-intensity ZI stimulation facilitated gaze shifts, whereas ZI inactivation reduced novelty seeking. ZI-dependent novelty seeking was not regulated by neurons in the lateral habenula or by many dopamine neurons in the substantia nigra, traditionally associated with reward seeking. But the anterior ventral medial temporal cortex, an area important for object vision and memory, was a prominent source of novelty predictions. These data uncover a functional pathway in the primate brain that regulates novelty seeking.

A prefrontal network integrates preferences for advance information about uncertain rewards and punishments

Humans and animals can be strongly motivated to seek information to resolve uncertainty about rewards and punishments. In particular, despite its clinical and societal relevance, very little is known about information seeking about punishments. We show that attitudes toward information about punishments and rewards are distinct and separable at both behavioral and neuronal levels. We demonstrate the existence of prefrontal neuronal populations that anticipate opportunities to gain information in a relatively valence-specific manner, separately anticipating information about either punishments or rewards. These neurons are located in anatomically interconnected subregions of anterior cingulate cortex (ACC) and ventrolateral prefrontal cortex (vlPFC) in area 12o/47. Unlike ACC, vlPFC also contains a population of neurons that integrate attitudes toward both reward and punishment information, to encode the overall preference for information in a bivalent manner. This cortical network is well suited to mediate information seeking by integrating the desire to resolve uncertainty about multiple, distinct motivational outcomes.

Combining brain perturbation and neuroimaging in non-human primates

Brain perturbation studies allow detailed causal inferences of behavioral and neural processes. Because the combination of brain perturbation methods and neural measurement techniques is inherently challenging, research in humans has predominantly focused on non-invasive, indirect brain perturbations, or neurological lesion studies. Non-human primates have been indispensable as a neurobiological system that is highly similar to humans while simultaneously being more experimentally tractable, allowing visualization of the functional and structural impact of systematic brain perturbation. This review considers the state of the art in non-human primate brain perturbation with a focus on approaches that can be combined with neuroimaging. We consider both non-reversible (lesions) and reversible or temporary perturbations such as electrical, pharmacological, optical, optogenetic, chemogenetic, pathway-selective, and ultrasound based interference methods. Method-specific considerations from the research and development community are offered to facilitate research in this field and support further innovations. We conclude by identifying novel avenues for further research and innovation and by highlighting the clinical translational potential of the methods.

Using non-invasive neuroimaging to enhance the care, well-being and experimental outcomes of laboratory non-human primates (monkeys)

Over the past 10-20 years, neuroscience witnessed an explosion in the use of non-invasive imaging methods, particularly magnetic resonance imaging (MRI), to study brain structure and function. Simultaneously, with access to MRI in many research institutions, MRI has become an indispensable tool for researchers and veterinarians to guide improvements in surgical procedures and implants and thus, experimental as well as clinical outcomes, given that access to MRI also allows for improved diagnosis and monitoring for brain disease. As part of the PRIMEatE Data Exchange, we gathered expert scientists, veterinarians, and clinicians who treat humans, to provide an overview of the use of non-invasive imaging tools, primarily MRI, to enhance experimental and welfare outcomes for laboratory non-human primates engaged in neuroscientific experiments. We aimed to provide guidance for other researchers, scientists and veterinarians in the use of this powerful imaging technology as well as to foster a larger conversation and community of scientists and veterinarians with a shared goal of improving the well-being and experimental outcomes for laboratory animals.

A neural network for information seeking

Humans and other animals often show a strong desire to know the uncertain rewards their future has in store, even when they cannot use this information to influence the outcome. However, it is unknown how the brain predicts opportunities to gain information and motivates this information-seeking behavior. Here we show that neurons in a network of interconnected subregions of primate anterior cingulate cortex and basal ganglia predict the moment of gaining information about uncertain rewards. Spontaneous increases in their information prediction signals are followed by gaze shifts toward objects associated with resolving uncertainty, and pharmacologically disrupting this network reduces the motivation to seek information. These findings demonstrate a cortico-basal ganglia mechanism responsible for motivating actions to resolve uncertainty by seeking knowledge about the future.

Animals resolve uncertainty by seeking knowledge about the future. How the brain controls this is unclear. The authors show that a network including primate anterior cingulate cortex and basal ganglia encodes opportunities to gain information about uncertain rewards and mediates information seeking.

Going with the Flow: The Neural Mechanisms Underlying Illusions of Complex-Flow Motion

Studying the mismatch between perception and reality helps us better understand the constructive nature of the visual brain. The Pinna-Brelstaff motion illusion is a compelling example illustrating how a complex moving pattern can generate an illusory motion perception. When an observer moves toward (expansion) or away (contraction) from the Pinna-Brelstaff figure, the figure appears to rotate. The neural mechanisms underlying the illusory complex-flow motion of rotation, expansion, and contraction remain unknown. We studied this question at both perceptual and neuronal levels in behaving male macaques by using carefully parametrized Pinna-Brelstaff figures that induce the above motion illusions. We first demonstrate that macaques perceive illusory motion in a manner similar to that of human observers. Neurophysiological recordings were subsequently performed in the middle temporal area (MT) and the dorsal portion of the medial superior temporal area (MSTd). We find that subgroups of MSTd neurons encoding a particular global pattern of real complex-flow motion (rotation, expansion, contraction) also represent illusory motion patterns of the same class. They require an extra 15 ms to reliably discriminate the illusion. In contrast, MT neurons encode both real and illusory local motions with similar temporal delays. These findings reveal that illusory complex-flow motion is first represented in MSTd by the same neurons that normally encode real complex-flow motion. However, the extraction of global illusory motion in MSTd from other classes of real complex-flow motion requires extra processing time. Our study illustrates a cascaded integration mechanism from MT to MSTd underlying the transformation from external physical to internal nonveridical flow-motion perception.SIGNIFICANCE STATEMENT The neural basis of the transformation from objective reality to illusory percepts of rotation, expansion, and contraction remains unknown. We demonstrate psychophysically that macaques perceive these illusory complex-flow motions in a manner similar to that of human observers. At the neural level, we show that medial superior temporal (MSTd) neurons represent illusory flow motions as if they were real by globally integrating middle temporal area (MT) local motion signals. Furthermore, while MT neurons reliably encode real and illusory local motions with similar temporal delays, MSTd neurons take a significantly longer time to process the signals associated with illusory percepts. Our work extends previous complex-flow motion studies by providing the first detailed analysis of the neuron-specific mechanisms underlying complex forms of illusory motion integration from MT to MSTd.

Novelty, Salience, and Surprise Timing Are Signaled by Neurons in the Basal Forebrain

The basal forebrain (BF) is a principal source of modulation of the neocortex [1-6] and is thought to regulate cognitive functions such as attention, motivation, and learning by broadcasting information about salience [2, 3, 5, 7-19]. However, events can be salient for multiple reasons-such as novelty, surprise, or reward prediction errors [20-24]-and to date, precisely which salience-related information the BF broadcasts is unclear. Here, we report that the primate BF contains at least two types of neurons that often process salient events in distinct manners: one with phasic burst responses to cues predicting salient events and one with ramping activity anticipating such events. Bursting neurons respond to cues that convey predictions about the magnitude, probability, and timing of primary reinforcements. They also burst to the reinforcement itself, particularly when it is unexpected. However, they do not have a selective response to reinforcement omission (the unexpected absence of an event). Thus, bursting neurons do not convey value-prediction errors but do signal surprise associated with external events. Indeed, they are not limited to processing primary reinforcement: they discriminate fully expected novel visual objects from familiar objects and respond to object-sequence violations. In contrast, ramping neurons predict the timing of many salient, novel, and surprising events. Their ramping activity is highly sensitive to the subjects' confidence in event timing and on average encodes the subjects' surprise after unexpected events occur. These data suggest that the primate BF contains mechanisms to anticipate the timing of a diverse set of important external events (via ramping activity) and to rapidly deploy cognitive resources when these events occur (via short latency bursting).

Probing Sensory Readout via Combined Choice-Correlation Measures and Microstimulation Perturbation

It is controversial whether covariation between neuronal activity and perceptual choice (i.e., choice correlation) reflects the functional readout of sensory signals. Here, we combined choice-correlation measures and electrical microstimulation on a site-to-site basis in the medial superior temporal area (MST), middle temporal area (MT), and ventral intraparietal area (VIP) when macaques discriminated between motion directions in both fine and coarse tasks. Microstimulation generated comparable effects between tasks but heterogeneous effects across and within brain regions. Within the MST and MT, microstimulation significantly biased an animal's choice toward the sensory preference instead of choice-related signals of the stimulated units. This was particularly evident for sites with conflict preference of sensory and choice-related signals. In the VIP, microstimulation failed to produce significant effects in either task despite strong choice correlations presented in this area. Our results suggest that sensory readout may not be inferred from choice-related signals during perceptual decision-making tasks.

A simple, inexpensive method for subcortical stereotactic targeting in nonhuman primates

BACKGROUND

Many current neuroscience studies in large animal models have focused on recordings from cortical structures. While sufficient for analyzing sensorimotor systems, many processes are modulated by subcortical nuclei. Large animal models, such as nonhuman primates (NHP), provide an optimal model for studying these circuits, but the ability to target subcortical structures has been hampered by lack of a straightforward approach to targeting.

NEW METHOD

Here we present a method of subcortical targeting in NHP that uses MRI-compatible titanium screws as fiducials. The in vivo study used a cellular marker for histologic confirmation of accuracy.

RESULTS

Histologic results are presented showing a cellular stem cell marker within targeted structures, with mean errors ± standard deviations (SD) of 1.40 ± 1.19 mm in the X-axis and 0.9 ± 0.97 mm in the Z-axis. The Y-axis errors ± SD ranged from 1.5 ± 0.43 to 4.2 ± 1.72 mm.

COMPARISON WITH EXISTING METHODS

This method is easy and inexpensive, and requires no fabrication of equipment, keeping in mind the goal of optimizing a technique for implantation or injection into multiple interconnected areas.

CONCLUSION

This procedure will enable primate researchers to target deep, subcortical structures more precisely in animals of varying ages and weights.

Multiple Mechanisms for Processing Reward Uncertainty in the Primate Basal Forebrain

The ability to use information about the uncertainty of future outcomes is critical for adaptive behavior in an uncertain world. We show that the basal forebrain (BF) contains at least two distinct neural-coding strategies to support this capacity. The dorsal-lateral BF, including the ventral pallidum (VP), contains reward-sensitive neurons, some of which are selectively suppressed by uncertain-reward predictions (U(-)). In contrast, the medial BF (mBF) contains reward-sensitive neurons, some of which are selectively enhanced (U(+)) by uncertain-reward predictions. In a two-alternative choice-task, U(-) neurons were selectively suppressed while monkeys chose uncertain options over certain options. During the same choice-epoch, U(+) neurons signaled the subjective reward value of the choice options. Additionally, after the choice was reported, U(+) neurons signaled reward uncertainty until the choice outcome. We suggest that uncertainty-related suppression of VP may participate in the mediation of uncertainty-seeking actions, whereas uncertainty-related enhancement of the mBF may direct cognitive resources to monitor and learn from uncertain-outcomes.

SIGNIFICANCE STATEMENT

To survive in an uncertain world, we must approach uncertainty and learn from it. Here we provide evidence for two mostly distinct mechanisms for processing uncertainty about rewards within different subregions of the primate basal forebrain (BF). We found that uncertainty suppressed the representation of certain (or safe) reward values by some neurons in the dorsal-lateral BF, in regions occupied by the ventral pallidum. This uncertainty-related suppression was evident as monkeys made risky choices. We also found that uncertainty-enhanced the activity of many medial BF neurons, most prominently after the monkeys' choices were completed (as they awaited uncertain outcomes). Based on these findings, we propose that different subregions of the BF could support action and learning under uncertainty in distinct but complimentary manners.

Distributed Representation of Curvilinear Self-Motion in the Macaque Parietal Cortex

Information about translations and rotations of the body is critical for complex self-motion perception during spatial navigation. However, little is known about the nature and function of their convergence in the cortex. We measured neural activity in multiple areas in the macaque parietal cortex in response to three different types of body motion applied through a motion platform: translation, rotation, and combined stimuli, i.e., curvilinear motion. We found a continuous representation of motion types in each area. In contrast to single-modality cells preferring either translation-only or rotation-only stimuli, convergent cells tend to be optimally tuned to curvilinear motion. A weighted summation model captured the data well, suggesting that translation and rotation signals are integrated subadditively in the cortex. Interestingly, variation in the activity of convergent cells parallels behavioral outputs reported in human psychophysical experiments. We conclude that representation of curvilinear self-motion perception is widely distributed in the primate sensory cortex.

Neurons in the Primate Medial Basal Forebrain Signal Combined Information about Reward Uncertainty, Value, and Punishment Anticipation

It has been suggested that the basal forebrain (BF) exerts strong influences on the formation of memory and behavior. However, what information is used for the memory-behavior formation is unclear. We found that a population of neurons in the medial BF (medial septum and diagonal band of Broca) of macaque monkeys encodes a unique combination of information: reward uncertainty, expected reward value, anticipation of punishment, and unexpected reward and punishment. The results were obtained while the monkeys were expecting (often with uncertainty) a rewarding or punishing outcome during a Pavlovian procedure, or unexpectedly received an outcome outside the procedure. In vivo anterograde tracing using manganese-enhanced MRI suggested that the major recipient of these signals is the intermediate hippocampal formation. Based on these findings, we hypothesize that the medial BF identifies various contexts and outcomes that are critical for memory processing in the hippocampal formation.

Selective and graded coding of reward uncertainty by neurons in the primate anterodorsal septal region

Natural environments are uncertain. Uncertainty of emotional outcomes can induce anxiety and raise vigilance, promote and signal the opportunity for learning, modulate economic choice and regulate risk-seeking. Here we demonstrate that a subset of neurons in the anterodorsal region of the primate septum (ADS) are primarily devoted to processing uncertainty in a highly specific manner. Those neurons were selectively activated by visual cues indicating probabilistic delivery of reward (for example, 25%, 50% and 75% reward) and did not respond to cues indicating certain outcomes (0% and 100% reward). The average ADS uncertainty response was graded with the magnitude of reward uncertainty and selectively signaled uncertainty about rewards rather than punishments. The selective and graded information about reward uncertainty encoded by many neurons in the ADS may underlie modulation of uncertainty of value- and sensorimotor-related areas to regulate goal-directed behavior.