Variable cardiac responses in rhesus macaque monkeys after discrete mediodorsal thalamus manipulations

The control of some physiological parameters, such as the heart rate, is known to have a role in cognitive and emotional processes. Cardiac changes are also linked to mental health issues and neurodegeneration. Thus, it is not surprising that many of the brain structures typically associated with cognition and emotion also comprise a circuit-the central automatic network-responsible for the modulation of cardiovascular output. The mediodorsal thalamus (MD) is involved in higher cognitive processes and is also known to be connected to some of the key neural structures that regulate cardiovascular function. However, it is unclear whether the MD has any role in this circuitry. Here, we show that discrete manipulations (microstimulation during anaesthetized functional neuroimaging or localized cytotoxin infusions) to either the magnocellular or the parvocellular MD subdivisions led to observable and variable changes in the heart rate of female and male rhesus macaque monkeys. Considering the central positions that these two MD subdivisions have in frontal cortico-thalamocortical circuits, our findings suggest that MD contributions to autonomic regulation may interact with its identified role in higher cognitive processes, representing an important physiological link between cognition and emotion.

Convergence of location, direction, and theta in the rat anteroventral thalamic nucleus

The thalamus and cortex are anatomically interconnected, with the thalamus providing integral information for cortical functions. The anteroventral thalamic nucleus (AV) is reciprocally connected to retrosplenial cortex (RSC). Two distinct AV subfields, dorsomedial (AVDM) and ventrolateral (AVVL), project differentially to granular vs. dysgranular RSC, respectively. To probe if functional responses of AV neurons differ, we recorded single neurons and local field potentials from AVDM and AVVL in rats during foraging. We observed place cells (neurons modulated by spatial location) in both AVDM and AVVL. Additionally, we characterized neurons modulated by theta oscillations, heading direction, and a conjunction of these. Place cells and conjunctive Theta-by-Head direction cells were more prevalent in AVVL; more non-conjunctive theta and directional neurons were prevalent in AVDM. These findings add further evidence that there are two thalamocortical circuits connecting AV and RSC, and reveal that the signaling involves place information in addition to direction and theta.

Trends and Treatment Approaches for Complications in Neuroscience Experiments with Monkey Species

Our goal in this manuscript is to advance the assessment and treatment of monkey species in neuroscience research. We hope to begin a discussion and establish baseline data on how complications are identified and treated. We surveyed the neuroscience research community working with monkeys and compiled responses to questions about investigator demographics, assessment of animal wellbeing, treatment choices, and approaches to mitigate risks associated with CNS procedures and promote monkey health and wellbeing. The majority of the respondents had worked with nonhuman primates (NHP) for over 15 y. Identification of procedure-related complications and efficacy of treatment generally rely on common behavioral indices. Treatments for localized inflammatory responses are generally successful, whereas the treatment success for meningitis or meningoencephalitis, abscesses, and hemorrhagic stroke are less successful. Behavioral signs of pain are treated successfully with NSAIDs and opioids. Our future plans are to collate treatment protocols and develop best practices that can be shared across the neuroscience community to improve treatment success rates and animal welfare and therefore science. Human protocols can be used to develop best practices, assess outcomes, and promote further refinements in treatment practices for monkeys to enhance research outcomes.

Structural Connectivity Changes After Fornix Transection in Macaques Using Probabilistic Diffusion Tractography

The fornix, the limbic system's white matter tract connecting the extended hippocampal system to subcortical structures of the medial diencephalon, is strongly associated with learning and memory in humans and nonhuman primates (NHPs). Here, we sought to investigate alterations in structural connectivity across key cortical and subcortical regions after fornix transection in NHPs. We collected diffusion-weighted MRI (dMRI) data from three macaque monkeys that underwent bilateral fornix transection during neurosurgery and from four age- and cohort-matched control macaques that underwent surgery to implant a head-post but remained neurologically intact. dMRI data were collected from both groups at two time points, before and after the surgeries, and scans took place at around the same time for the two groups. We used probabilistic tractography and employed the number of tracking streamlines to quantify connectivity across our regions of interest (ROIs), in all dMRI sessions. In the neurologically intact monkeys, we observed high connectivity across certain ROIs, including the CA3 hippocampal subfield with the retrosplenial cortex (RSC), the anterior thalamus with the RSC, and the RSC with the anterior cingulate cortex (ACC). However, we found that, compared to the control group, the fornix-transected monkeys showed marked, significant, connectivity changes including increases between the anterior thalamus and the ACC and between the CA3 and the ACC, as well as decreases between the CA3 and the RSC. Our results highlight cortical and subcortical network changes after fornix transection and identify candidate indirect connectivity routes that may support memory functions after damage and/or neurodegeneration.

Cortico-thalamocortical interactions for learning, memory and decision-making

The thalamus and cortex are interconnected both functionally and anatomically and share a common developmental trajectory. Interactions between the mediodorsal thalamus (MD) and different parts of the prefrontal cortex are essential in cognitive processes, such as learning and adaptive decision-making. Cortico-thalamocortical interactions involving other dorsal thalamic nuclei, including the anterior thalamus and pulvinar, also influence these cognitive processes. Our work, and that of others, indicates a crucial influence of these interdependent cortico-thalamocortical neural networks that contributes actively to the processing of information within the cortex. Each of these thalamic nuclei also receives potent subcortical inputs that are likely to provide additional influences on their regulation of cortical activity. Here, we highlight our current neuroscientific research aimed at establishing when cortico-MD thalamocortical neural network communication is vital within the context of a rapid learning and memory discrimination task. We are collecting evidence of MD-prefrontal cortex neural network communication in awake, behaving male rhesus macaques. Given the prevailing evidence, further studies are needed to identify both broad and specific mechanisms that govern how the MD, anterior thalamus and pulvinar cortico-thalamocortical interactions support learning, memory and decision-making. Current evidence shows that the MD (and the anterior thalamus) are crucial for frontotemporal communication, and the pulvinar is crucial for frontoparietal communication. Such work is crucial to advance our understanding of the neuroanatomical and physiological bases of these brain functions in humans. In turn, this might offer avenues to develop effective treatment strategies to improve the cognitive deficits often observed in many debilitating neurological disorders and diseases and in neurodegeneration.

Visualizing advances in the future of primate neuroscience research

Future neuroscience and biomedical projects involving non-human primates (NHPs) remain essential in our endeavors to understand the complexities and functioning of the mammalian central nervous system. In so doing, the NHP neuroscience researcher must be allowed to incorporate state-of-the-art technologies, including the use of novel viral vectors, gene therapy and transgenic approaches to answer continuing and emerging research questions that can only be addressed in NHP research models. This perspective piece captures these emerging technologies and some specific research questions they can address. At the same time, we highlight some current caveats to global NHP research and collaborations including the lack of common ethical and regulatory frameworks for NHP research, the limitations involving animal transportation and exports, and the ongoing influence of activist groups opposed to NHP research.

Mediodorsal Thalamus Is Critical for Updating during Extradimensional Shifts But Not Reversals in the Attentional Set-Shifting Task

Cognitive flexibility, attributed to frontal cortex, is vital for navigating the complexities of everyday life. The mediodorsal thalamus (MD), interconnected to frontal cortex, may influence cognitive flexibility. Here, male rats performed an attentional set-shifting task measuring intradimensional (ID) and extradimensional (ED) shifts in sensory discriminations. MD lesion rats needed more trials to learn the rewarded sensory dimension. However, once the choice response strategy was established, learning further two-choice discriminations in the same sensory dimension, and reversals of the reward contingencies in the same dimension, were unimpaired. Critically though, MD lesion rats were impaired during the ED shift, when they must rapidly update the optimal choice response strategy. Behavioral analyses showed MD lesion rats had significantly reduced correct within-trial second choice responses. This evidence shows that transfer of information via the MD is critical when rapid within-trial updates in established choice response strategies are required after a rule change.

Evidence for two distinct thalamocortical circuits in retrosplenial cortex

Retrosplenial cortex (RSC) lies at the interface between sensory and cognitive networks in the brain and mediates between these, although it is not yet known how. It has two distinct subregions, granular (gRSC) and dysgranular (dRSC). The present study investigated how these subregions differ with respect to their electrophysiology and thalamic connectivity, as a step towards understanding their functions. The gRSC is more closely connected to the hippocampal formation, in which theta-band local field potential oscillations are prominent. We, therefore, compared theta-rhythmic single-unit activity between the two RSC subregions and found, mostly in gRSC, a subpopulation of non-directional cells with spiking activity strongly entrained by theta oscillations, suggesting a stronger coupling of gRSC to the hippocampal system. We then used retrograde tracers to test for differential inputs to RSC from the anteroventral thalamus (AV). We found that gRSC and dRSC differ in their afferents from two AV subfields: dorsomedial (AVDM) and ventrolateral (AVVL). Specifically: (1) as a whole AV projects more strongly to gRSC; (2) AVVL targets both gRSC and dRSC, while AVDM provides a selective projection to gRSC, (3) the gRSC projection is layer-specific: AVDM targets specifically gRSC superficial layers. These same AV projections are topographically organized with ventral AV neurons innervating rostral RSC and dorsal AV neurons innervating caudal RSC. These combined results suggest the existence of two distinct but interacting RSC subcircuits: one connecting AVDM to gRSC that may comprise part of the cognitive hippocampal system, and the other connecting AVVL to both RSC regions that may link hippocampal and perceptual regions. We suggest that these subcircuits are distinct to allow for differential weighting during integration of converging sensory and cognitive computations: an integration that may take place in thalamus, RSC, or both.

The continued need for animals to advance brain research

Policymakers aim to move toward animal-free alternatives for scientific research and have introduced very strict regulations for animal research. We argue that, for neuroscience research, until viable and translational alternatives become available and the value of these alternatives has been proven, the use of animals should not be compromised.

Thalamocortical interactions in cognition and disease: the mediodorsal and anterior thalamic nuclei

The mediodorsal thalamus (MD) and anterior thalamic nuclei (ATN) are two adjacent brain nodes that support our ability to make decisions, learn, update information, form and retrieve memories, and find our way around. The MD and PFC work in partnerships to support cognitive processes linked to successful learning and decision-making, while the ATN and extended hippocampal system together coordinate the encoding and retrieval of memories and successful spatial navigation. Yet, while these distinctions may appear to be segregated, both the MD and ATN together support our higher cognitive functions as they regulate and are influenced by interconnected fronto-temporal neural networks and subcortical inputs. Our review focuses on recent studies in animal models and in humans. This evidence is re-shaping our understanding of the importance of MD and ATN cortico-thalamocortical pathways in influencing complex cognitive functions. Given the evidence from clinical settings and neuroscience research labs, the MD and ATN should be considered targets for effective treatments in neuropsychiatric diseases and disorders and neurodegeneration.

International primate neuroscience research regulation, public engagement and transparency opportunities

Scientific excellence is a necessity for progress in biomedical research. As research becomes ever more international, establishing international collaborations will be key to advancing our scientific knowledge. Understanding the similarities in standards applied by different nations to animal research, and where the differences might lie, is crucial. Cultural differences and societal values will also contribute to these similarities and differences between countries and continents. Our overview is not comprehensive for all species, but rather focuses on non-human primate (NHP) research, involving New World marmosets and Old World macaques, conducted in countries where NHPs are involved in neuroimaging research. Here, an overview of the ethics and regulations is provided to help assess welfare standards amongst primate research institutions. A comparative examination of these standards was conducted to provide a basis for establishing a common set of standards for animal welfare. These criteria may serve to develop international guidelines, which can be managed by an International Animal Welfare and Use Committee (IAWUC). Internationally, scientists have a moral responsibility to ensure excellent care and welfare of their animals, which in turn, influences the quality of their research. When working with animal models, maintaining a high quality of care ("culture of care") and welfare is essential. The transparent promotion of this level of care and welfare, along with the results of the research and its impact, may reduce public concerns associated with animal experiments in neuroscience research.

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.

Protective cranial implant caps for macaques

BACKGROUND

Neuroscience studies with macaque monkeys may require cranial implants to stabilize the head or gain access to the brain for scientific purposes. Wound management that promotes healing after the cranial implant surgery in non-human primates can be difficult as it is not necessarily possible to cover the wound margins.

NEW METHOD

Here, we developed an easily modifiable head cap that protects the sutured skin margins after cranial implant surgery and contributes to wound healing. The protective head cap was developed in response to monkeys picking at sutured skin margins around an implant, complicating healing. The user-friendly protective cap, made from Klarity- R™ Sheet (3.2 mm thick with 36 % or 42 % perforation) is affixed to the implant post-surgically. Once secured and while the monkey is still anesthetized, the plastic sheeting is molded around the implant. The protective head cap restricts the monkey's finger access to its' wound margins while allowing air to circulate to promote wound healing.

RESULTS AND COMPARISON WITH EXISTING METHODS

Across two UK primate facilities, the protective head cap promoted wound healing. In monkeys that did not wear the head cap, re-suturing was necessary in ∼30 % of cases. In contrast, none of the monkeys that wore the head cap required re-suturing. The monkeys wearing the head cap also had reduced numbers of days of prescribed antibiotics and analgesia.

CONCLUSION

This bespoken, easily adaptable, protective head cap supports postoperative wound healing, and enhances the welfare of monkeys involved in neuroscience research.

Current Research in Neurobiology, an experimental platform for innovation

Welcome to Current Research in Neurobiology (CRNEUR), the gold open access, sibling journal to Current Opinion in Neurobiology, a journal for timely original research in neuroscience. At its very core, CRNEUR is a journal for creativity and innovation in science and publishing. As a journal, we ambitiously aim for CRNEUR to be a vehicle for what many of us envisioned an academic journal could be. Empowered by our commitment to fairness and transparency—to hold ourselves and others to a higher standard—here we describe our ambitions for innovation going forward. We need your help in this process and welcome your views via this survey (https://www.surveymonkey.co.uk/r/5LHWTML) and on social media (to start or join a discussion please use the hashtag #CRNEUR).

Corticocortical and Thalamocortical Changes in Functional Connectivity and White Matter Structural Integrity after Reward-Guided Learning of Visuospatial Discriminations in Rhesus Monkeys

The frontal cortex and temporal lobes together regulate complex learning and memory capabilities. Here, we collected resting-state functional and diffusion-weighted MRI data before and after male rhesus macaque monkeys received extensive training to learn novel visuospatial discriminations (reward-guided learning). We found functional connectivity changes in orbitofrontal, ventromedial prefrontal, inferotemporal, entorhinal, retrosplenial, and anterior cingulate cortices, the subicular complex, and the dorsal, medial thalamus. These corticocortical and thalamocortical changes in functional connectivity were accompanied by related white matter structural alterations in the uncinate fasciculus, fornix, and ventral prefrontal tract: tracts that connect (sub)cortical networks and are implicated in learning and memory processes in monkeys and humans. After the well-trained monkeys received fornix transection, they were impaired in learning new visuospatial discriminations. In addition, the functional connectivity profile that was observed after the training was altered. These changes were accompanied by white matter changes in the ventral prefrontal tract, although the integrity of the uncinate fasciculus remained unchanged. Our experiments highlight the importance of different communication relayed among corticocortical and thalamocortical circuitry for the ability to learn new visuospatial associations (learning-to-learn) and to make reward-guided decisions.SIGNIFICANCE STATEMENT Frontal neural networks and the temporal lobes contribute to reward-guided learning in mammals. Here, we provide novel insight by showing that specific corticocortical and thalamocortical functional connectivity is altered after rhesus monkeys received extensive training to learn novel visuospatial discriminations. Contiguous white matter fiber pathways linking these gray matter structures, namely, the uncinate fasciculus, fornix, and ventral prefrontal tract, showed structural changes after completing training in the visuospatial task. Additionally, different patterns of functional and structural connectivity are reported after removal of subcortical connections within the extended hippocampal system, via fornix transection. These results highlight the importance of both corticocortical and thalamocortical interactions in reward-guided learning in the normal brain and identify brain structures important for memory capabilities after injury.

Considering the Evidence for Anterior and Laterodorsal Thalamic Nuclei as Higher Order Relays to Cortex

Our memories are essential in our daily lives. The frontal and cingulate cortices, hippocampal system and medial temporal lobes are key brain regions. In addition, severe amnesia also occurs after damage or dysfunction to the anterior thalamic nuclei; this subcortical thalamic hub is interconnected to these key cortical memory structures. Behavioral, anatomical, and physiological evidence across mammalian species has shown that interactions between the anterior thalamic nuclei, cortex and hippocampal formation are vital for spatial memory processing. Furthermore, the adjacent laterodorsal thalamic nucleus (LD), interconnected to the retrosplenial cortex (RSC) and visual system, also contributes to spatial memory in mammals. However, how these thalamic nuclei contribute to memory still remains largely unknown. Fortunately, our understanding of the importance of the thalamus in cognitive processes is being redefined, as widespread evidence challenges the established view of the thalamus as a passive relay of sensory and subcortical information to the cortex. In this review article, we examine whether the anterior thalamic nuclei and the adjacent LD are suitable candidates for "higher-order" thalamic nuclei, as defined by the Sherman and Guillery model. Rather than simply relaying information to cortex, "higher-order" thalamic nuclei have a prominent role in cognition, as they can regulate how areas of the cortex interact with one another. These considerations along with a review of the latest research will be used to suggest future studies that will clarify the contributions that the anterior and LD have in supporting cortical functions during cognitive processes.

Preserved extrastriate visual network in a monkey with substantial, naturally occurring damage to primary visual cortex

Lesions of primary visual cortex (V1) lead to loss of conscious visual perception with significant impact on human patients. Understanding the neural consequences of such damage may aid the development of rehabilitation methods. In this rare case of a Rhesus macaque (monkey S), likely born without V1, the animal's in-group behaviour was unremarkable, but visual task training was impaired. With multi-modal magnetic resonance imaging, visual structures outside of the lesion appeared normal. Visual stimulation under anaesthesia with checkerboards activated lateral geniculate nucleus of monkey S, while full-field moving dots activated pulvinar. Visual cortical activation was sparse but included face patches. Consistently across lesion and control monkeys, functional connectivity analysis revealed an intact network of bilateral dorsal visual areas temporally correlated with V5/MT activation, even without V1. Despite robust subcortical responses to visual stimulation, we found little evidence for strengthened subcortical input to V5/MT supporting residual visual function or blindsight-like phenomena.

Effective chair training methods for neuroscience research involving rhesus macaques (Macaca mulatta)

BACKGROUND

Neuroscience research using macaques remains fundamental in our endeavours to understand how the human brain functions. Applying the refinement principle of the 3Rs is essential to optimise the monkeys' welfare and still produces high quality science.

NEW METHOD

Here we document refinements in our training methods for acclimation to transport devices (i.e. primate chair or transport box) while working with 46 male rhesus macaques. Our training methods always used positive reinforcement training (PRT). However, PRT was sometimes combined with negative reinforcement training (NRT), but not pole and collar techniques, to successfully transfer each monkey from its home enclosure to its transport device.

RESULTS AND COMPARISON WITH EXISTING METHODS

Training monkeys in pairs or groups, and starting their PRT training upon arrival within the unit reduced the days required to acclimate them. While the use of PRT is essential to establish a positive relationship with monkeys, NRT techniques are sometimes necessary, and are most effective when withdrawn immediately once the monkey makes the desired response, to reduce the days of acclimation. Once acclimatised to their chair, monkeys succeeded within 10 days to present their head voluntarily for neck-plating using PRT. Space reducers inside the chairs also facilitated head presentations for some monkeys.

CONCLUSIONS

Acclimating (shaping) the monkeys to transport devices can be a stressful experience for monkeys and trainers. The adaptations to our training substantially reduced the days spent on this stage. We view this reduction in days as an effective implementation of the 3Rs (refinement) in monkey neuroscience research.

The Regulatory Role of the Human Mediodorsal Thalamus

The function of the human mediodorsal thalamic nucleus (MD) has so far eluded a clear definition in terms of specific cognitive processes and tasks. Although it was at first proposed to play a role in long-term memory, a set of recent studies in animals and humans has revealed a more complex, and broader, role in several cognitive functions. The MD seems to play a multifaceted role in higher cognitive functions together with the prefrontal cortex and other cortical and subcortical brain areas. Specifically, we propose that the MD is involved in the regulation of cortical networks especially when the maintenance and temporal extension of persistent activity patterns in the frontal lobe areas are required.

Continued need for non-human primate neuroscience research

Neuroscience research in non-human primates (NHPs) has delivered fundamental knowledge about human brain function as well as some valuable therapies that have improved the lives of human patients with a variety of brain disorders. Research using NHPs, although it is facing serious challenges, continues to complement studies in human volunteers and patients, and will continue to be needed as the burdens of mental health problems and neurodegenerative diseases increase. At the same time, research into the 3Rs is helping to ameliorate the harms experienced by NHPs in experimental procedures, allowing the effective combination of optimal welfare conditions for the NHPs and high quality research.

Functional reorganisation and recovery following cortical lesions: A preliminary study in macaque monkeys

Damage following traumatic brain injury or stroke can often extend beyond the boundaries of the initial insult and can lead to maladaptive cortical reorganisation. On the other hand, beneficial cortical reorganisation leading to recovery of function can also occur. We used resting state FMRI to investigate how cortical networks in the macaque brain change across time in response to lesions to the prefrontal cortex, and how this reorganisation correlated with changes in behavioural performance in cognitive tasks. After prelesion testing and scanning, two monkeys received a lesion to regions surrounding the left principal sulcus followed by periodic testing and scanning. Later, the animals received another lesion to the opposite hemisphere and additional testing and scanning. Following the first lesion, we observed both a behavioural impairment and decrease in functional connectivity, predominantly in frontal-frontal networks. Approximately 8 weeks later, performance and connectivity patterns both improved. Following the second lesion, we observed a further behavioural deficit and decrease in connectivity that showed little recovery. We discuss how different mechanisms including alternate behavioural strategies and reorganisation of specific prefrontal networks may have led to improvements in behaviour. Further work will be needed to confirm these mechanisms.

Macaque parvocellular mediodorsal thalamus: dissociable contributions to learning and adaptive decision-making

Distributed brain networks govern adaptive decision‐making, new learning and rapid updating of information. However, the functional contribution of the rhesus macaque monkey parvocellular nucleus of the mediodorsal thalamus (MDpc) in these key higher cognitive processes remains unknown. This study investigated the impact of MDpc damage in cognition. Preoperatively, animals were trained on an object‐in‐place scene discrimination task that assesses rapid learning of novel information within each session. Bilateral neurotoxic (NMDA and ibotenic acid) MDpc lesions did not impair new learning unless the monkey had also sustained damage to the magnocellular division of the MD (MDmc). Contralateral unilateral MDpc and MDmc damage also impaired new learning, while selective unilateral MDmc damage produced new learning deficits that eventually resolved with repeated testing. In contrast, during food reward (satiety) devaluation, monkeys with either bilateral MDpc damage or combined MDpc and MDmc damage showed attenuated food reward preferences compared to unoperated control monkeys; the selective unilateral MDmc damage left performance intact. Our preliminary results demonstrate selective dissociable roles for the two adjacent nuclei of the primate MD, namely, MDpc, as part of a frontal cortical network, and the MDmc, as part of a frontal‐temporal cortical network, in learning, memory and the cognitive control of behavioural choices after changes in reward value. Moreover, the functional cognitive deficits produced after differing MD damage show that the different subdivisions of the MD thalamus support distributed neural networks to rapidly and fluidly incorporate task‐relevant information, in order to optimise the animals’ ability to receive rewards.

Retrosplenial cortex and its role in spatial cognition

Retrosplenial cortex is a region within the posterior neocortical system, heavily interconnected with an array of brain networks, both cortical and subcortical, that is, engaged by a myriad of cognitive tasks. Although there is no consensus as to its precise function, evidence from both human and animal studies clearly points to a role in spatial cognition. However, the spatial processing impairments that follow retrosplenial cortex damage are not straightforward to characterise, leading to difficulties in defining the exact nature of its role. In this article, we review this literature and classify the types of ideas that have been put forward into three broad, somewhat overlapping classes: (1) learning of landmark location, stability and permanence; (2) integration between spatial reference frames; and (3) consolidation and retrieval of spatial knowledge (schemas). We evaluate these models and suggest ways to test them, before briefly discussing whether the spatial function may be a subset of a more general function in episodic memory.

Cognitive Functions and Neurodevelopmental Disorders Involving the Prefrontal Cortex and Mediodorsal Thalamus

The mediodorsal nucleus of the thalamus (MD) has been implicated in executive functions (such as planning, cognitive control, working memory, and decision-making) because of its significant interconnectivity with the prefrontal cortex (PFC). Yet, whilst the roles of the PFC have been extensively studied, how the MD contributes to these cognitive functions remains relatively unclear. Recently, causal evidence in monkeys has demonstrated that in everyday tasks involving rapid updating (e.g., while learning something new, making decisions, or planning the next move), the MD and frontal cortex are working in close partnership. Furthermore, researchers studying the MD in rodents have been able to probe the underlying mechanisms of this relationship to give greater insights into how the frontal cortex and MD might interact during the performance of these essential tasks. This review summarizes the circuitry and known neuromodulators of the MD, and considers the most recent behavioral, cognitive, and neurophysiological studies conducted in monkeys and rodents; in total, this evidence demonstrates that MD makes a critical contribution to cognitive functions. We propose that communication occurs between the MD and the frontal cortex in an ongoing, fluid manner during rapid cognitive operations, via the means of efference copies of messages passed through transthalamic routes; the conductance of these messages may be modulated by other brain structures interconnected to the MD. This is similar to the way in which other thalamic structures have been suggested to carry out forward modeling associated with rapid motor responding and visual processing. Given this, and the marked thalamic pathophysiology now identified in many neuropsychiatric disorders, we suggest that changes in the different subdivisions of the MD and their interconnections with the cortex could plausibly give rise to a number of the otherwise disparate symptoms (including changes to olfaction and cognitive functioning) that are associated with many different neuropsychiatric disorders. In particular, we will focus here on the cognitive symptoms of schizophrenia and suggest testable hypotheses about how changes to MD-frontal cortex interactions may affect cognitive processes in this disorder.

Critical role for the mediodorsal thalamus in permitting rapid reward-guided updating in stochastic reward environments

Adaptive decision-making uses information gained when exploring alternative options to decide whether to update the current choice strategy. Magnocellular mediodorsal thalamus (MDmc) supports adaptive decision-making, but its causal contribution is not well understood. Monkeys with excitotoxic MDmc damage were tested on probabilistic three-choice decision-making tasks. They could learn and track the changing values in object-reward associations, but they were severely impaired at updating choices after reversals in reward contingencies or when there were multiple options associated with reward. These deficits were not caused by perseveration or insensitivity to negative feedback though. Instead, monkeys with MDmc lesions exhibited an inability to use reward to promote choice repetition after switching to an alternative option due to a diminished influence of recent past choices and the last outcome to guide future behavior. Together, these data suggest MDmc allows for the rapid discovery and persistence with rewarding options, particularly in uncertain or changing environments.

DOI:http://dx.doi.org/10.7554/eLife.13588.001

A small structure deep inside the brain, called the mediodorsal thalamus, is a critical part of a brain network that is important for learning new information and making decisions. However, the exact role of this brain area is still not understood, and there is little evidence showing that this area is actually needed to make the best choices.

To explore the role of this area further, Chakraborty et al. trained macaque monkeys to choose between three colorful objects displayed on a touchscreen that was controlled by a computer. Some of their choices resulted in the monkeys getting a tasty food pellet as a reward. However the probability of receiving a reward changed during testing, and in some cases, reversed, meaning that the highest rewarded object was no longer rewarded when chosen and vice versa. While at first the monkeys did not know which choice was the right one, they quickly learned and changed their choices during the test according to which option resulted in them receiving the most reward.

Next, the mediodorsal thalamus in each monkey was damaged and the tests were repeated. Previous research had suggested that such damage might result in animals repeatedly choosing the same option, even though it is clearly the wrong choice. However, Chakraborty et al. showed that it is not as simple as that. Instead monkeys with damage to the mediodorsal thalamus could make different choices but they struggled to use information from their most recent choices to best guide their future behavior. Specifically, the pattern of the monkeys’ choices suggests that the mediodorsal thalamus helps to quickly link recent choices that resulted in a reward in order to allow an individual to choose the best option as their next choice.

Further studies are now needed to understand the messages that are relayed between the mediodorsal thalamus and interconnected areas during this rapid linking of recent choices, rewards and upcoming decisions. This will help reveal how these brain areas support normal thought processes and how these processes might be altered in mental health disorders involving learning information and making decisions.

DOI:http://dx.doi.org/10.7554/eLife.13588.002

Retrosplenial Cortical Contributions to Anterograde and Retrograde Memory in the Monkey

Primate retrosplenial cortex (RSC) is important for memory but patient neuropathologies are diffuse so its key contributions to memory remain elusive. This study provides the first causal evidence that RSC in macaque monkeys is crucial for postoperative retention of preoperatively and postoperatively acquired memories. Preoperatively, monkeys learned 300 object-in-place scene discriminations across sessions. After RSC removal, one-trial postoperative retention tests revealed significant retrograde memory loss for these 300 discriminations relative to unoperated control monkeys. Less robust evidence was found for a deficit in anterograde memory (new postoperative learning) after RSC lesions as new learning to criterion measures failed to reveal any significant learning impairment. However, after achieving ≥90% learning criterion for the postoperatively presented novel 100 object-in-place scene discriminations, short-term retention (i.e., measured after 24 h delay) of this well-learnt set was impaired in the RSC monkeys relative to controls. A further experiment assessed rapid "within" session acquisition of novel object-in-place scene discriminations, again confirming that new learning per se was unimpaired by bilateral RSC removal. Primate RSC contributes critically to memory by supporting normal retention of information, even when this information does not involve an autobiographical component.

Connectivity between the superior colliculus and the amygdala in humans and macaque monkeys: virtual dissection with probabilistic DTI tractography

It has been suggested that some cortically blind patients can process the emotional valence of visual stimuli via a fast, subcortical pathway from the superior colliculus (SC) that reaches the amygdala via the pulvinar. We provide in vivo evidence for connectivity between the SC and the amygdala via the pulvinar in both humans and rhesus macaques. Probabilistic diffusion tensor imaging tractography revealed a streamlined path that passes dorsolaterally through the pulvinar before arcing rostrally to traverse above the temporal horn of the lateral ventricle and connect to the lateral amygdala. To obviate artifactual connectivity with crossing fibers of the stria terminalis, the stria was also dissected. The putative streamline between the SC and amygdala traverses above the temporal horn dorsal to the stria terminalis and is positioned medial to it in humans and lateral to it in monkeys. The topography of the streamline was examined in relation to lesion anatomy in five patients who had previously participated in behavioral experiments studying the processing of emotionally valenced visual stimuli. The pulvinar lesion interrupted the streamline in two patients who had exhibited contralesional processing deficits and spared the streamline in three patients who had no deficit. Although not definitive, this evidence supports the existence of a subcortical pathway linking the SC with the amygdala in primates. It also provides a necessary bridge between behavioral data obtained in future studies of neurological patients, and any forthcoming evidence from more invasive techniques, such as anatomical tracing studies and electrophysiological investigations only possible in nonhuman species.

Adaptability to changes in temporal structure is fornix-dependent

Recognition memory deficits, even after short delays, are sometimes observed following hippocampal damage. One hypothesis links the hippocampus with processes in updating contextual memory representation. Here, we used fornix transection, which partially disconnects the hippocampal system, and compares the performance of fornix-transected monkeys with normal monkeys on two versions of a delayed-matching-to-position task with short delays. Spatial recognition memory was affected by fornix transection only when the temporal structure of the task changed across trials, while differences in motor control, motivation, perception, or short-term memory were not critical. We attributed the deficit to a compromised ability in tracking changes in task temporal structure.

Behavioral and cognitive changes after early postnatal lesions of the rat mediodorsal thalamus

Early insults to the thalamus result in functional and/or structural abnormalities in the cerebral cortex. However, differences in behavioral and cognitive changes after early insult are not well characterized. The present study assessed whether early postnatal damage to mediodorsal nucleus of the thalamus (MD), reciprocally interconnected with the prefrontal cortex, causes behavioral and cognitive alterations in young adult rats. Rat pups at postnatal day 4 received bilateral electrolytic lesion of MD, or a MD Sham lesion or were anesthetized controls; on recovery they were returned to their mothers until weaning. Seven weeks later, all rats were tested with the following behavioral and cognitive paradigms: T-maze test, open field test, actimetry, elevated plus maze test, social interactions test and passive avoidance test. Rats with bilateral MD damage presented with disrupted recognition memory, deficits in shifting response rules, significant hypoactivity, increased anxiety-like behavior, deficits in learning associations as well as decreased locomotor activity, and reduced social interactions compared to MD Sham lesion and anesthetized Control rats. The lesion also caused significant decreases in pyramidal cell density in three frontal cortex regions: medial infralimbic cortex, dorsolateral anterior cortex, and cingulate Cg1 cortex. The present findings suggest a functional role for MD in the postnatal maturation of affective behavior. Further some of the behavioral and cognitive alterations observed in these young adult rats after early MD lesion are reminiscent of those present in major psycho-affective disorders, such as schizophrenia in humans.

Evidence for Mediodorsal Thalamus and Prefrontal Cortex Interactions during Cognition in Macaques

It is proposed that mediodorsal thalamus contributes to cognition via interactions with prefrontal cortex. However, there is relatively little evidence detailing the interactions between mediodorsal thalamus and prefrontal cortex linked to cognition in primates. This study investigated these interactions during learning, memory, and decision-making tasks in rhesus monkeys using a disconnection lesion approach. Preoperatively, monkeys learned object-in-place scene discriminations embedded within colorful visual backgrounds. Unilateral neurotoxic lesions to magnocellular mediodorsal thalamus (MDmc) impaired the ability to learn new object-in-place scene discriminations. In contrast, unilateral ablations to ventrolateral and orbital prefrontal cortex (PFv+o) left learning intact. A second unilateral MDmc or PFv+o lesion in the contralateral hemisphere to the first operation, causing functional MDmc–PFv+o disconnection across hemispheres, further impaired learning object-in-place scene discriminations, although object discrimination learning remained intact. Adaptive decision-making after reward satiety devaluation was also reduced. These data highlight the functional importance of interactions between MDmc and PFv+o during learning object-in-place scene discriminations and adaptive decision-making but not object discrimination learning. Moreover, learning deficits observed after unilateral removal of MDmc but not PFv+o provide direct behavioral evidence of the MDmc role influencing more widespread regions of the frontal lobes in cognition.

The mediodorsal thalamus as a higher order thalamic relay nucleus important for learning and decision-making

Recent evidence from monkey models of cognition shows that the magnocellular subdivision of the mediodorsal thalamus (MDmc) is more critical for learning new information than for retention of previously acquired information. Further, consistent evidence in animal models shows the mediodorsal thalamus (MD) contributes to adaptive decision-making. It is assumed that prefrontal cortex (PFC) and medial temporal lobes govern these cognitive processes so this evidence suggests that MD contributes a role in these cognitive processes too. Anatomically, the MD has extensive excitatory cortico-thalamo-cortical connections, especially with the PFC. MD also receives modulatory inputs from forebrain, midbrain and brainstem regions. It is suggested that the MD is a higher order thalamic relay of the PFC due to the dual cortico-thalamic inputs from layer V ('driver' inputs capable of transmitting a message) and layer VI ('modulator' inputs) of the PFC. Thus, the MD thalamic relay may support the transfer of information across the PFC via this indirect thalamic route. This review summarizes the current knowledge about the anatomy of MD as a higher order thalamic relay. It also reviews behavioral and electrophysiological studies in animals to consider how MD might support the transfer of information across the cortex during learning and decision-making. Current evidence suggests the MD is particularly important during rapid trial-by-trial associative learning and decision-making paradigms that involve multiple cognitive processes. Further studies need to consider the influence of the MD higher order relay to advance our knowledge about how the cortex processes higher order cognition.

A neural circuit covarying with social hierarchy in macaques

Despite widespread interest in social dominance, little is known of its neural correlates in primates. We hypothesized that social status in primates might be related to individual variation in subcortical brain regions implicated in other aspects of social and emotional behavior in other mammals. To examine this possibility we used magnetic resonance imaging (MRI), which affords the taking of quantitative measurements noninvasively, both of brain structure and of brain function, across many regions simultaneously. We carried out a series of tests of structural and functional MRI (fMRI) data in 25 group-living macaques. First, a deformation-based morphometric (DBM) approach was used to show that gray matter in the amygdala, brainstem in the vicinity of the raphe nucleus, and reticular formation, hypothalamus, and septum/striatum of the left hemisphere was correlated with social status. Second, similar correlations were found in the same areas in the other hemisphere. Third, similar correlations were found in a second data set acquired several months later from a subset of the same animals. Fourth, the strength of coupling between fMRI-measured activity in the same areas was correlated with social status. The network of subcortical areas, however, had no relationship with the sizes of individuals' social networks, suggesting the areas had a simple and direct relationship with social status. By contrast a second circuit in cortex, comprising the midsuperior temporal sulcus and anterior and dorsal prefrontal cortex, covaried with both individuals' social statuses and the social network sizes they experienced. This cortical circuit may be linked to the social cognitive processes that are taxed by life in more complex social networks and that must also be used if an animal is to achieve a high social status.

What does the mediodorsal thalamus do?

Dense amnesia can result from damage to the medial diencephalon in humans and in animals. In humans this damage is diffuse and can include the mediodorsal nuclei of the thalamus. In animal models, lesion studies have confirmed the mediodorsal thalamus (MD) has a role in memory and other cognitive tasks, although the extent of deficits is mixed. Anatomical tracing studies confirm at least three different subgroupings of the MD: medial, central, and lateral, each differentially interconnected to the prefrontal cortex (PFC). Moreover, these subgroupings of the MD also receive differing inputs from other brain structures, including the basal ganglia thus the MD subgroupings form key nodes in interconnected frontal-striatal-thalamic neural circuits, integrating critical information within the PFC. We will provide a review of data collected from non-human primates and rodents after selective brain injury to the whole of the MD as well as these subgroupings to highlight the extent of deficits in various cognitive tasks. This research highlights the neural basis of memory and cognitive deficits associated with the subgroupings of the MD and their interconnected neural networks. The evidence shows that the MD plays a critical role in many varied cognitive processes. In addition, the MD is actively processing information and integrating it across these neural circuits for successful cognition. Having established that the MD is critical for memory and cognition, further research is required to understand how the MD specifically influences these cognitive processing carried out by the brain.

Ventrolateral prefrontal cortex is required for performance of a strategy implementation task but not reinforcer devaluation effects in rhesus monkeys

The ability to apply behavioral strategies to obtain rewards efficiently and make choices based on changes in the value of rewards is fundamental to the adaptive control of behavior. The extent to which different regions of the prefrontal cortex are required for specific kinds of decisions is not well understood. We tested rhesus monkeys with bilateral ablations of the ventrolateral prefrontal cortex on tasks that required the use of behavioral strategies to optimize the rate with which rewards were accumulated, or to modify choice behavior in response to changes in the value of particular rewards. Monkeys with ventrolateral prefrontal lesions were impaired in performing the strategy-based task, but not on value-based decision-making. In contrast, orbital prefrontal ablations produced the opposite impairments in the same tasks. These findings support the conclusion that independent neural systems within the prefrontal cortex are necessary for control of choice behavior based on strategies or on stimulus value.

Dissociable roles for cortical and subcortical structures in memory retrieval and acquisition

The relationship between anterograde and retrograde amnesia remains unclear. Previous data from both clinical neuropsychology and monkey lesion studies suggest that damage to discrete subcortical structures leads to a relatively greater degree of anterograde than retrograde amnesia, whereas damage to discrete regions of cortex leads to the opposite pattern of impairments. Nevertheless, damage to the medial diencephalon in humans is associated with both retrograde and anterograde amnesia. In the present study, we sought to reconcile this by assessing retention as well as subsequent relearning and new postoperative learning. Rhesus monkeys learned 300 unique scene discriminations preoperatively, and retention was assessed in a preoperative and postoperative one-trial retrieval test. Combined bilateral subcortical lesions to the magnocellular mediodorsal thalamus and fornix impaired postoperative retention of the preoperatively acquired information. In addition, subsequent relearning and new postoperative learning were also impaired. This contrasts with the effects of a discrete lesion to just one of these structures, after which retention is intact in both cases. Discrete bilateral ablations to the entorhinal cortex impaired retention but had no effect on new learning. Combined with previous work from our laboratory, these results support the hypothesis that subcortical damage has a relatively greater effect on new learning, and cortical damage has a relatively greater effect on retention. Furthermore, the results demonstrate that retrograde amnesia occurs as a result of subcortical damage only if it is widespread, leading to an extensive disruption of cortical functioning. Damage of this nature may account for dense amnesia.

Dorsolateral prefrontal lesions do not impair tests of scene learning and decision-making that require frontal-temporal interaction

Theories of dorsolateral prefrontal cortex (DLPFC) involvement in cognitive function variously emphasize its involvement in rule implementation, cognitive control, or working and/or spatial memory. These theories predict broad effects of DLPFC lesions on tests of visual learning and memory. We evaluated the effects of DLPFC lesions (including both banks of the principal sulcus) in rhesus monkeys on tests of scene learning and strategy implementation that are severely impaired following crossed unilateral lesions of frontal cortex and inferotemporal cortex. Dorsolateral lesions had no effect on learning of new scene problems postoperatively, or on the implementation of preoperatively acquired strategies. They were also without effect on the ability to adjust choice behaviour in response to a change in reinforcer value, a capacity that requires interaction between the amygdala and frontal lobe. These intact abilities following DLPFC damage support specialization of function within the prefrontal cortex, and suggest that many aspects of memory and strategic and goal-directed behaviour can survive ablation of this structure.

Perseverative interference with object-in-place scene learning in rhesus monkeys with bilateral ablation of ventrolateral prefrontal cortex

Surgical disconnection of the frontal cortex and inferotemporal cortex severely impairs many aspects of visual learning and memory, including learning of new object-in-place scene memory problems, a monkey model of episodic memory. As part of a study of specialization within prefrontal cortex in visual learning and memory, we tested monkeys with bilateral ablations of ventrolateral prefrontal cortex in object-in-place scene learning. These monkeys were mildly impaired in scene learning relative to their own preoperative performance, similar in severity to that of monkeys with bilateral ablation of orbital prefrontal cortex. An analysis of response types showed that the monkeys with lesions were specifically impaired in responding to negative feedback during learning: The post-operative increase in errors was limited to trials in which the first response to each new problem, made on the basis of trial and error, was incorrect. This perseverative pattern of deficit was not observed in the same analysis of response types in monkeys with bilateral ablations of the orbital prefrontal cortex, who were equally impaired on trials with correct and incorrect first responses. This may represent a specific signature of ventrolateral prefrontal involvement in episodic learning and memory.

Neurotoxic lesions of ventrolateral prefrontal cortex impair object-in-place scene memory

Disconnection of the frontal lobe from the inferotemporal cortex produces deficits in a number of cognitive tasks that require the application of memory-dependent rules to visual stimuli. The specific regions of frontal cortex that interact with the temporal lobe in performance of these tasks remain undefined. One capacity that is impaired by frontal–temporal disconnection is rapid learning of new object-in-place scene problems, in which visual discriminations between two small typographic characters are learned in the context of different visually complex scenes. In the present study, we examined whether neurotoxic lesions of ventrolateral prefrontal cortex in one hemisphere, combined with ablation of inferior temporal cortex in the contralateral hemisphere, would impair learning of new object-in-place scene problems. Male macaque monkeys learned 10 or 20 new object-in-place problems in each daily test session. Unilateral neurotoxic lesions of ventrolateral prefrontal cortex produced by multiple injections of a mixture of ibotenate and N-methyl-d-aspartate did not affect performance. However, when disconnection from inferotemporal cortex was completed by ablating this region contralateral to the neurotoxic prefrontal lesion, new learning was substantially impaired. Sham disconnection (injecting saline instead of neurotoxin contralateral to the inferotemporal lesion) did not affect performance. These findings support two conclusions: first, that the ventrolateral prefrontal cortex is a critical area within the frontal lobe for scene memory; and second, the effects of ablations of prefrontal cortex can be confidently attributed to the loss of cell bodies within the prefrontal cortex rather than to interruption of fibres of passage through the lesioned area.

Lateral and anterior thalamic lesions impair independent memory systems

Damage to the medial region of the thalamus, both in clinical cases (e.g., patients with infarcts or the Korsakoff's syndrome) and animal lesion models, is associated with variable amnesic deficits. Some studies suggest that many of these memory deficits rely on the presence of lateral thalamic lesions (LT) that include the intralaminar nuclei, presumably by altering normal function between the striatum and frontal cortex. Other studies suggest that the anterior thalamic nuclei (AT) may be more critical, as a result of disruption to an extended hippocampal system. Here, highly selective LT and AT lesions were made to test the prediction that these two regions contribute to two different memory systems. Only LT lesions produced deficits on a preoperatively acquired response-related (egocentric) working memory task, tested in a cross-maze. Conversely, only AT lesions impaired postoperative acquisition of spatial working memory, tested in a radial maze. These findings provide the first direct evidence of a double dissociation between the LT and AT neural aggregates. As the lateral and the anterior medial thalamus influence parallel independent memory processing systems, they may each contribute to memory deficits, depending on lesion extent in clinical and experimental cases of thalamic amnesia.

Dissociable memory effects after medial thalamus lesions in the rat

Variable neuropathology in cases of diencephalic amnesia has led to uncertainty in identifying key thalamic nuclei and their potential role in learning and memory. Based on the principal neural connections of the medial thalamus, the current study tested the hypothesis that different aggregates of thalamic nuclei contribute to separate memory systems. Lesions of the anterior thalamic aggregate (AT), which comprises the anterodorsal, anteromedial and anteroventral nuclei produced substantial deficits in both working and reference spatial memory in a radial arm maze task in rats, supporting the view that the AT is an integral part of a hippocampal memory system. Lesions to the lateral thalamic aggregate (LT), which comprises the intralaminar nuclei (centrolateral, paracentral and rostral central medial nuclei) and lateral mediodorsal thalamic nuclei (lateral and paralamellar nuclei) produced a mild working memory impairment only, while lesions to the posteromedial thalamic aggregate (MT), which comprises the central and medial mediodorsal thalamic nuclei and the intermediodorsal nucleus had no effect on radial arm maze performance. In contrast, only MT lesions impaired learning associated with memory for reward value, consistent with the idea that the MT contributes to an amygdala memory system. Compared with chance discrimination, the control and AT groups, but not MT or LT groups, showed evidence for temporal order memory for two recently presented objects; all groups showed intact object recognition for novel vs. familiar objects. These new dissociations show that different medial thalamic aggregates participate in multiple memory systems and reinforce the idea that memory deficits in diencephalic amnesics may vary as a function of the relative involvement of different thalamic regions.

Spatial working memory and the brainstem cholinergic innervation to the anterior thalamus

The anteroventral thalamic nucleus (AV) has a role in spatial memory, but the influence of the prominent brainstem cholinergic projection to this region is unknown. Here, spatial memory in a 12-arm radial maze was examined after 0.15 microl bilateral AV infusions of scopolamine. In part one, rats visited six arms singly (the phase 1 arms) and, after a 10 min delay, were allowed free choice to both phase 1 arms and the remaining six baited arms (phase 2 arms). Scopolamine (10 microg) administered during the delay increased errors to both phase 1 and phase 2 arms, whereas PBS infusions increased phase 1 arm errors only. The PBS effect was the result of inserting the internal cannulas alone and not the infusion. The same dose of scopolamine (10 microg) infused before maze testing (part two: no phase 1 arms, no delay) also impaired spatial memory over and above the effects of both PBS and no-infusion, which did not differ markedly. Part two also showed that choice latency and choice strategies were unaffected by PBS and scopolamine. Cannulation and infusion procedures in both parts one and two did not produce any negative carryover effects across multiple control (no internal cannula) sessions, and a trypan blue manipulation indicated that infusions were restricted to the AV region. This study provides the first direct evidence that the brainstem cholinergic innervation to the limbic thalamus influences learning and memory, which may have important implications for human neurological conditions such as alcohol-related disorders and schizophrenia.

A cost-effectiveness approach to drug subsidy and pricing in Australia

The Australian government offers its citizens subsidies on a select list of pharmaceuticals. For a drug to qualify for inclusion on this list, its manufacturer must demonstrate that the drug is both clinically effective and cost-effective. In part, this measure, along with others, was introduced to improve clinical and economic outcomes. Although this evidence-based system has provided transparency and consistency in decision making about which drugs will be covered, it may not have contained the rate of increase in drug costs.

Problems with the interpretation of pharmacoeconomic analyses: a review of submissions to the Australian Pharmaceutical Benefits Scheme

CONTEXT

Pharmacoeconomic analyses are being used increasingly as the basis for reimbursement of the costs of new drugs. Reports of these analyses are often published in peer-reviewed journals. However, the analyses are complex and difficult to evaluate.

OBJECTIVE

To describe the nature of problems encountered in the evaluation and interpretation of pharmacoeconomic analyses used as a basis for reimbursement decisions.

DATA SOURCES

All major submissions to the Department of Health and Aged Care (DHAC) by the pharmaceutical industry for funding made under the Australian Pharmaceutical Benefits Scheme. Specifically, the DHAC's database of submissions that were received between January 1994 and December 1997 were reviewed.

STUDY SELECTION

Of a total of 326 submissions, 218 had serious problems of interpretation and were included in the analysis. The nature of the serious problems reviewed were classified as estimates of comparative clinical efficacy, comparator issues, modeling issues, and calculation errors.

DATA EXTRACTION

All submissions in the DHAC's database were reviewed and data were extracted if both the DHAC evaluators and technical subcommittee considered problems to have a significant bearing on the decisions of the parent committee.

DATA SYNTHESIS

Of a total of 326 submissions, 218 (67%) had significant problems and 31 had more than 1 problem. Of the 249 problems identified, 154 (62%) related to uncertainty in the estimates of comparative clinical efficacy, and 71 (28.5%) related to modeling issues, which included clinical assumptions or cost estimates, used in the construction of the economic models. There were 15 instances of disagreement over the choice of comparator, and serious calculation errors were found on 9 occasions. Overall, 159 problems (64%) were considered to be avoidable.

CONCLUSIONS

Significant problems were identified in these pharmacoeconomic analyses. The intensive evaluation process used in the Australian Pharmaceutical Benefits Scheme allowed for identification and correction of pharmacoecomomic analysis problems, but the resources that are required may be beyond the capacity of many organizations, including peer-reviewed journals.

Lack of evidence for improvement in internal mammary graft flow by occlusion of side branch

Coronary steal due to unligated side branches of an internal mammary artery graft has been reported previously. Embolization of these side branches has been shown to result in symptomatic improvement, but objective evidence of improved flow to the coronary artery has been lacking. We studied intracoronary Doppler flow in a patient presenting with symptoms thought to be due to a large unligated side branch of mammary graft. There was no significant change in the mammary flow after balloon occlusion of the side branch. More objective data may be required to routinely prescribe side branch embolization for symptomatic patients with unligated side branches of a mammary graft.

Profiles of antibacterial drug use in Australia and trends from 1987 to 1989. A report from the Drug Utilization Subcommittee of the Pharmaceutical Benefits Advisory Committee

OBJECTIVE

To survey the use by Australian pensioners of orally administered antimicrobial agents supplied through the Pharmaceutical Benefits Scheme over the years 1987-1989.

DATA SOURCES

Australian Pharmaceutical Benefits Scheme pensioner data for 1987-1989 and market research data from a private company.

DATA EXTRACTION

The data were initially available as the number of prescriptions dispensed and were aggregated on a quarter year basis. These were converted to defined daily doses (DDDs) per 1000 pensioners per day (DDD/1000 per day). This conversion of the data allows comparisons across drug groups, and with prescribing patterns in other countries. The DDD/1000 per day also gives an indication of the proportion of individuals in the community receiving a drug at a particular time.

DATA SYNTHESIS

There was a 26% increase in antibacterial drug use over this period. Comparison of prescribing profiles for particular indications with peer consensus guidelines revealed marked discrepancies, particularly for upper respiratory tract infections, urinary tract infections, otitis media and sinusitis. Upper respiratory tract infections accounted for 31% of instances of antibiotic prescribing. Dispensing of amoxycillin/potassium clavulanate relative to amoxycillin as a single agent, showed a marked increase in 1989 to the point where it represented 25% of all amoxycillin used. This could be considered excessive given the lack of evidence that amoxycillin resistance has substantially increased in infections presenting to general practice. The data presented here confirm previous suggestions that Australian antibiotic prescribing is heavily concentrated on the use of broad spectrum agents. By comparison with Norway or Sweden, there is a greater relative use of broad spectrum penicillins and tetracyclines and a lower relative use of phenoxymethylpenicillin and trimethoprim.

CONCLUSIONS

Antibiotic prescribing practices in Australia continue to be often inappropriate and expensive, being directed too heavily towards the use of broad spectrum agents and newer more expensive drugs. Correction of such antibacterial drug use will require coordination of educational and regulatory activities that are sensitive to the context of general practice.

The effect of cardiac catheterization upon management of advanced aortic and mitral valve disease

We assessed the incremental effect of cardiac catheterization upon the management of 93 adult patients with aortic and/or mitral valve disease, referred for surgical consideration. There were 52 patients with aortic valve disease, 29 with mitral valve disease and 12 with aortic and mitral valve disease. Prior to cardiac catheterization, a detailed unblinded ultrasound assessment of each valve was made utilizing 2D and Doppler ultrasound. Based upon the ultrasound result and the clinical assessment, the patient's cardiologist recorded a grading of valve severity and a management decision for each valve. Following catheterization and coronary angiography, the cardiologist repeated the gradings of valve severity and recorded a final management decision. After catheterization, management changed in nine patients and was unchanged in 84. Reasons for management change included differences between echocardiographic and catheterization assessment of valvular regurgitation (three patients), information on coronary anatomy (two patients), minor differences in assessed aortic valve area (one patient) and left ventricular function (one patient), and confirmation of ultrasound findings where clinical and ultrasound findings had been conflicting before catheterization (two patients). Both mitral and aortic valve disease were present in the three patients in whom management changed as a result of significant differences between echocardiography and catheterization assessment of valvular regurgitation. Management was unchanged in the 16 patients with isolated mitral stenosis. In this study, a combination of clinical and noninvasive assessment including Doppler echocardiography, resulted in a reliable evaluation of valvular disease in a large majority of patients.(ABSTRACT TRUNCATED AT 250 WORDS)