Neuronal Coding of Serial Order: Syntax of Grooming in the Neostriatum

A novel naïve Bayes approach to identifying grooming behaviors in the force-plate actometric platform

BACKGROUND

Self-grooming behavior in rodents serves as a valuable behavioral index for investigating stereotyped and perseverative responses. Most current grooming analyses rely on video observation, which lacks standardization, efficiency, and quantitative information about force. To address these limitations, we developed an automated paradigm to analyze grooming using a force-plate actometer.

NEW METHOD

Grooming behavior is quantified by calculating ratios of relevant movement power spectral bands. These ratios are input into a naïve Bayes classifier, trained with manual video observations. The effectiveness of this method was tested using CIN-d mice, an animal model developed through early-life depletion of striatal cholinergic interneurons (CIN-d) and featuring prolonged grooming responses to acute stressors. Behavioral monitoring was simultaneously conducted on the force-place actometer and by video recording.

RESULTS

The naïve Bayes approach achieved 93.7% accurate classification and an area under the receiver operating characteristic curve of 0.894. We confirmed that male CIN-d mice displayed significantly longer grooming durations than controls. However, this elevation was not correlated with increases in grooming force. Notably, the dopaminergic antagonist haloperidol reduced grooming force and duration.

COMPARISON WITH EXISTING METHODS

In contrast to observation-based approaches, our method affords rapid, unbiased, and automated assessment of grooming duration, frequency, and force.

CONCLUSIONS

Our novel approach enables fast and accurate automated detection of grooming behaviors. This method holds promise for high-throughput assessments of grooming stereotypies in animal models of neuropsychiatric disorders.

Role of the basal ganglia in innate and learned behavioural sequences

Integrating individual actions into coherent, organised behavioural units, a process called chunking, is a fundamental, evolutionarily conserved process that renders actions automatic. In vertebrates, evidence points to the basal ganglia - a complex network believed to be involved in action selection - as a key component of action sequence encoding, although the underlying mechanisms are only just beginning to be understood. Central pattern generators control many innate automatic behavioural sequences that form some of the most basic behaviours in an animal's repertoire, and in vertebrates, brainstem and spinal pattern generators are under the control of higher order structures such as the basal ganglia. Evidence suggests that the basal ganglia play a crucial role in the concatenation of simpler behaviours into more complex chunks, in the context of innate behavioural sequences such as chain grooming in rats, as well as sequences in which innate capabilities and learning interact such as birdsong, and sequences that are learned from scratch, such as lever press sequences in operant behaviour. It has been proposed that the role of the striatum, the largest input structure of the basal ganglia, might lie in selecting and allowing the relevant central pattern generators to gain access to the motor system in the correct order, while inhibiting other behaviours. As behaviours become more complex and flexible, the pattern generators seem to become more dependent on descending signals. Indeed, during learning, the striatum itself may adopt the functional characteristics of a higher order pattern generator, facilitated at the microcircuit level by striatal neuropeptides.

Striatal ensemble activity in an innate naturalistic behavior

Self-grooming is an innate, naturalistic behavior found in a wide variety of organisms. The control of rodent grooming has been shown to be mediated by the dorsolateral striatum through lesion studies and in-vivo extracellular recordings. Yet, it is unclear how populations of neurons in the striatum encode grooming. We recorded single-unit extracellular activity from populations of neurons in freely moving mice and developed a semi-automated approach to detect self-grooming events from 117 hours of simultaneous multi-camera video recordings of mouse behavior. We first characterized the grooming transition-aligned response profiles of striatal projection neuron and fast spiking interneuron single units. We identified striatal ensembles whose units were more strongly correlated during grooming than during the entire session. These ensembles display varied grooming responses, including transient changes around grooming transitions or sustained changes in activity throughout the duration of grooming. Neural trajectories computed from the identified ensembles retain the grooming related dynamics present in trajectories computed from all units in the session. These results elaborate striatal function in rodent self-grooming and demonstrate that striatal grooming-related activity is organized within functional ensembles, improving our understanding of how the striatum guides action selection in a naturalistic behavior.

B-SOiD, an open-source unsupervised algorithm for identification and fast prediction of behaviors

Studying naturalistic animal behavior remains a difficult objective. Recent machine learning advances have enabled limb localization; however, extracting behaviors requires ascertaining the spatiotemporal patterns of these positions. To provide a link from poses to actions and their kinematics, we developed B-SOiD - an open-source, unsupervised algorithm that identifies behavior without user bias. By training a machine classifier on pose pattern statistics clustered using new methods, our approach achieves greatly improved processing speed and the ability to generalize across subjects or labs. Using a frameshift alignment paradigm, B-SOiD overcomes previous temporal resolution barriers. Using only a single, off-the-shelf camera, B-SOiD provides categories of sub-action for trained behaviors and kinematic measures of individual limb trajectories in any animal model. These behavioral and kinematic measures are difficult but critical to obtain, particularly in the study of rodent and other models of pain, OCD, and movement disorders.

Blocking NK1 receptors disrupts the sequential and temporal organization of chain grooming in rats

The basal ganglia are a group of sub-cortical structures believed to play a critical role in action selection and sequencing. The striatum is the largest input structure of the basal ganglia and contains the neuropeptide substance P in abundance. Recent computational work has suggested that substance P could play a critical role in action sequence performance and acquisition, but this has not been tested experimentally before. The aim of the present study was to test how blocking substance P's main NK1-type receptors affected the sequential and temporal organization of spontaneous behavioral patterns. We did this in rats by focusing on the grooming chain, an innate and highly stereotyped ordered sequence. We performed an open field experiment in which the NK1 receptor antagonist L-733,060 was injected intraperitoneally in rats at two doses (2 and 4 mg/kg/ml), in a within-subject counterbalanced design. We used first order transition probabilities, Variable Length Markov Models, entropy metrics and T-pattern analysis to evaluate the effects of L-733,060 on sequential and temporal aspects of spontaneously ordered behavioral sequences. Our results suggest that blocking NK1 receptors made the transitions between the grooming chain elements significantly more variable, the transition structure of the grooming bouts simpler, and it increased the probability of transitioning from active to inactive states. Overall, this suggest that blocking substance P receptors led to a general break down in the fluency of spontaneous behavioral sequences, suggesting that substance P could be playing a key role in the implementation of sequential patterns.

Cortical and striatal circuits together encode transitions in natural behavior

In natural behavior, we fluidly change from one type of activity to another in a sequence of motor actions. Corticostriatal circuits are thought to have a particularly important role in the construction of action sequences, but neuronal coding of a sequential behavior consisting of different motor programs has not been investigated at the circuit level in corticostriatal networks, making the exact nature of this involvement elusive. Here, we show, by analyzing spontaneous self-grooming in rats, that neuronal modulation in motor cortex and dorsal striatum is strongly related to transitions between behaviors. Our data suggest that longer action sequences in rodent grooming behavior emerge from stepwise control of individual behavioral transitions, where future actions are encoded differently depending on current motor state. This state-dependent motor coding was found to differentiate between rare behavioral transitions and as opposed to more habitual sequencing of actions.

Non-motor Characterization of the Basal Ganglia: Evidence From Human and Non-human Primate Electrophysiology

Although the basal ganglia have been implicated in a growing list of human behaviors, they include some of the least understood nuclei in the brain. For several decades studies have employed numerous methodologies to uncover evidence pointing to the basal ganglia as a hub of both motor and non-motor function. Recently, new electrophysiological characterization of the basal ganglia in humans has become possible through direct access to these deep structures as part of routine neurosurgery. Electrophysiological approaches for identifying non-motor function have the potential to unlock a deeper understanding of pathways that may inform clinical interventions and particularly neuromodulation. Various electrophysiological modalities can also be combined to reveal functional connections between the basal ganglia and traditional structures throughout the neocortex that have been linked to non-motor behavior. Several reviews have previously summarized evidence for non-motor function in the basal ganglia stemming from behavioral, clinical, computational, imaging, and non-primate animal studies; in this review, instead we turn to electrophysiological studies of non-human primates and humans. We begin by introducing common electrophysiological methodologies for basal ganglia investigation, and then we discuss studies across numerous non-motor domains–emotion, response inhibition, conflict, decision-making, error-detection and surprise, reward processing, language, and time processing. We discuss the limitations of current approaches and highlight the current state of the information.

The Striatum Organizes 3D Behavior via Moment-to-Moment Action Selection

Many naturalistic behaviors are built from modular components that are expressed sequentially. Although striatal circuits have been implicated in action selection and implementation, the neural mechanisms that compose behavior in unrestrained animals are not well understood. Here, we record bulk and cellular neural activity in the direct and indirect pathways of dorsolateral striatum (DLS) as mice spontaneously express action sequences. These experiments reveal that DLS neurons systematically encode information about the identity and ordering of sub-second 3D behavioral motifs; this encoding is facilitated by fast-timescale decorrelations between the direct and indirect pathways. Furthermore, lesioning the DLS prevents appropriate sequence assembly during exploratory or odor-evoked behaviors. By characterizing naturalistic behavior at neural timescales, these experiments identify a code for elemental 3D pose dynamics built from complementary pathway dynamics, support a role for DLS in constructing meaningful behavioral sequences, and suggest models for how actions are sculpted over time.

M-Track: A New Software for Automated Detection of Grooming Trajectories in Mice

Grooming is a complex and robust innate behavior, commonly performed by most vertebrate species. In mice, grooming consists of a series of stereotyped patterned strokes, performed along the rostro-caudal axis of the body. The frequency and duration of each grooming episode is sensitive to changes in stress levels, social interactions and pharmacological manipulations, and is therefore used in behavioral studies to gain insights into the function of brain regions that control movement execution and anxiety. Traditional approaches to analyze grooming rely on manually scoring the time of onset and duration of each grooming episode, and are often performed on grooming episodes triggered by stress exposure, which may not be entirely representative of spontaneous grooming in freely-behaving mice. This type of analysis is time-consuming and provides limited information about finer aspects of grooming behaviors, which are important to understand movement stereotypy and bilateral coordination in mice. Currently available commercial and freeware video-tracking software allow automated tracking of the whole body of a mouse or of its head and tail, not of individual forepaws. Here we describe a simple experimental set-up and a novel open-source code, named M-Track, for simultaneously tracking the movement of individual forepaws during spontaneous grooming in multiple freely-behaving mice. This toolbox provides a simple platform to perform trajectory analysis of forepaw movement during distinct grooming episodes. By using M-track we show that, in C57BL/6 wild type mice, the speed and bilateral coordination of the left and right forepaws remain unaltered during the execution of distinct grooming episodes. Stress exposure induces a profound increase in the length of the forepaw grooming trajectories. M-Track provides a valuable and user-friendly interface to streamline the analysis of spontaneous grooming in biomedical research studies.

Review of available studies of the neurobiology and pharmacotherapeutic management of trichotillomania

Trichotillomania (TTM) is a psychiatric disorder characterized by an irresistible urge to pull out one's hair. Currently there are no FDA approved treatments for TTM, which makes it difficult for clinicians to select an appropriate therapeutic plan. The clinical studies that have been performed do not provide sufficient or consistent evidence regarding which drug classes should be administered. Unfortunately, most of the available data consist of case reports and clinical trials with limited sample size. This review provides an overview of currently available clinical literature that targets TTM. A summary of clinical trials as well as case reports is provided. The most common rating scales used for clinical assessment are also reviewed. The etiology of TTM remains unclear. Studies that examine various neuroanatomical, neurobiologic, as well as genetic factors associated with TTM are thoroughly discussed in this review. It is evident that clear understanding of TTM is crucial to provide better recognition, assessment, and treatment to patients of this disorder. Finally, despite research efforts for establishing pharmacological options for treatment, it is clear that new targets are warranted in order to ensure a clinically supported effective pharmacological approach to treat TTM.

Role of the striatum in language: Syntactic and conceptual sequencing

The basal ganglia (BG) have long been associated with cognitive control, and it is widely accepted that they also subserve an indirect, control role in language. Nevertheless, it cannot be completely ruled out that the BG may be involved in language in some domain-specific manner. The present study aimed to investigate one type of cognitive control-sequencing, a function that has long been connected with the BG-and to test whether the BG could be specifically implicated in language. Participants were required to rearrange materials sequentially based on linguistic (syntactic or conceptual) or non-linguistic (order switching) rules, or to repeat a previously ordered sequence as a control task. Functional magnetic resonance imaging (fMRI) data revealed a strongly active left-lateralized corticostriatal network, encompassing the anterior striatum, dorsolaterial and ventrolateral prefrontal cortex and presupplementary motor area, while the participants were sequencing materials using linguistic vs. non-linguistic rules. This functional network has an anatomical basis and is strikingly similar to the well-known associative loop implicated in sensorimotor sequence learning. We concluded that the anterior striatum has extended its original sequencing role and worked in concert with frontal cortical regions to subserve the function of linguistic sequencing in a domain-specific manner.

Nucleus accumbens GABAergic inhibition generates intense eating and fear that resists environmental retuning and needs no local dopamine

Intense fearful behavior and/or intense appetitive eating behavior can be generated by localized amino acid inhibitions along a rostrocaudal anatomical gradient within medial shell of nucleus accumbens of the rat. This can be produced by microinjections in medial shell of either the γ-aminobutyric acid (GABA)A agonist muscimol (mimicking intrinsic GABAergic inputs) or the AMPA (α-amino-3-hydroxy-5-methylisoxazole-4-propionic acid) antagonist DNQX (6,7-dinitroquinoxaline-2,3-dione), disrupting corticolimbic glutamate inputs). At rostral sites in medial shell, each drug robustly stimulates appetitive eating and food intake, whereas at more caudal sites the same drugs instead produce increasingly fearful behaviors such as escape, distress vocalizations and defensive treading (an antipredator behavior rodents emit to snakes and scorpions). Previously we showed that intense motivated behaviors generated by glutamate blockade require local endogenous dopamine and can be modulated in valence by environmental ambience. Here we investigated whether GABAergic generation of intense appetitive and fearful motivations similarly depends on local dopamine signals, and whether the valence of motivations generated by GABAergic inhibition can also be retuned by changes in environmental ambience. We report that the answer to both questions is 'no'. Eating and fear generated by GABAergic inhibition of accumbens shell does not need endogenous dopamine. Also, the appetitive/fearful valence generated by GABAergic muscimol microinjections resists environmental retuning and is determined almost purely by rostrocaudal anatomical placement. These results suggest that nucleus accumbens GABAergic release of fear and eating are relatively independent of modulatory dopamine signals, and more anatomically pre-determined in valence balance than release of the same intense behaviors by glutamate disruptions.

Prefrontal cortex modulates desire and dread generated by nucleus accumbens glutamate disruption

BACKGROUND

Corticolimbic circuits, including direct projections from prefrontal cortex to nucleus accumbens (NAc), permit top-down control of intense motivations generated by subcortical circuits. In rats, localized disruptions of glutamate signaling within medial shell of NAc generate desire or dread, anatomically organized along a rostrocaudal gradient analogous to a limbic keyboard. At rostral locations in shell, these disruptions generate appetitive eating, but at caudal locations the disruptions generate progressively fearful behaviors (distress vocalizations, escape attempts, and antipredator reactions). Here, we asked whether medial prefrontal cortex can modulate intense motivations generated by subcortical NAc disruptions.

METHODS

We used simultaneous microinjections in medial prefrontal cortex regions and in NAc shell to examine whether the desire or dread generated by NAc shell disruptions is modulated by activation/inhibition of three specific regions of prefrontal cortex: medial orbitofrontal cortex, infralimbic cortex (homologous to area 25 or subgenual anterior cingulate in the human), or prelimbic cortex (midventral anterior cingulate).

RESULTS

We found that activation of medial orbitofrontal cortex biased intense bivalent motivation in an appetitive direction by amplifying generation of eating behavior by middle to caudal NAc disruptions, without altering fear. In contrast, activation of infralimbic prefrontal cortex powerfully and generally suppressed both appetitive eating and fearful behaviors generated by NAc shell disruptions.

CONCLUSIONS

These results suggest that corticolimbic projections from discrete prefrontal regions can either bias motivational valence or generally suppress subcortically generated intense motivations of desire or fear.

Building a neuroscience of pleasure and well-being

BACKGROUND: How is happiness generated via brain function in lucky individuals who have the good fortune to be happy? Conceptually, well-being or happiness has long been viewed as requiring at least two crucial ingredients: positive affect or pleasure (hedonia) and a sense of meaningfulness or engagement in life (eudaimonia). Science has recently made progress in relating hedonic pleasure to brain function, and so here we survey new insights into how brains generate the hedonic ingredient of sustained or frequent pleasure. We also briefly discuss how brains might connect hedonia states of pleasure to eudaimonia assessments of meaningfulness, and so create balanced states of positive well-being. RESULTS: Notable progress has been made in understanding brain bases of hedonic processing, producing insights into that brain systems that cause and/or code sensory pleasures. Progress has been facilitated by the recognition that hedonic brain mechanisms are largely shared between humans and other mammals, allowing application of conclusions from animal studies to a better understanding of human pleasures. In the past few years, evidence has also grown to indicate that for humans, brain mechanisms of higher abstract pleasures strongly overlap with more basic sensory pleasures. This overlap may provide a window into underlying brain circuitry that generates all pleasures, including even the hedonic quality of pervasive well-being that detaches from any particular sensation to apply to daily life in a more sustained or frequent fashion. CONCLUSIONS: Hedonic insights are applied to understanding human well-being here. Our strategy combines new findings on brain mediators that generate the pleasure of sensations with evidence that human brains use many of the same hedonic circuits from sensory pleasures to create the higher pleasures. This in turn may be linked to how hedonic systems interact with other brain systems relevant to self-understanding and the meaning components of eudaimonic happiness. Finally, we speculate a bit about how brains that generate hedonia states might link to eudaimonia assessments to create properly balanced states of positive well-being that approach true happiness.

Hematopoietic origin of pathological grooming in Hoxb8 mutant mice

Mouse Hoxb8 mutants show unexpected behavior manifested by compulsive grooming and hair removal, similar to behavior in humans with the obsessive-compulsive disorder spectrum disorder trichotillomania. As Hox gene disruption often has pleiotropic effects, the root cause of this behavioral deficit was unclear. Here we report that, in the brain, Hoxb8 cell lineage exclusively labels bone marrow-derived microglia. Furthermore, transplantation of wild-type bone marrow into Hoxb8 mutant mice rescues their pathological phenotype. It has been suggested that the grooming dysfunction results from a nociceptive defect, also exhibited by Hoxb8 mutant mice. However, bone marrow transplant experiments and cell type-specific disruption of Hoxb8 reveal that these two phenotypes are separable, with the grooming phenotype derived from the hematopoietic lineage and the sensory defect derived from the spinal cord cells. Immunological dysfunctions have been associated with neuropsychiatric disorders, but the causative relationships are unclear. In this mouse, a distinct compulsive behavioral disorder is associated with mutant microglia.

The tempted brain eats: pleasure and desire circuits in obesity and eating disorders

What we eat, when and how much, all are influenced by brain reward mechanisms that generate "liking" and "wanting" for foods. As a corollary, dysfunction in reward circuits might contribute to the recent rise of obesity and eating disorders. Here we assess brain mechanisms known to generate "liking" and "wanting" for foods and evaluate their interaction with regulatory mechanisms of hunger and satiety, relevant to clinical issues. "Liking" mechanisms include hedonic circuits that connect together cubic-millimeter hotspots in forebrain limbic structures such as nucleus accumbens and ventral pallidum (where opioid/endocannabinoid/orexin signals can amplify sensory pleasure). "Wanting" mechanisms include larger opioid networks in nucleus accumbens, striatum, and amygdala that extend beyond the hedonic hotspots, as well as mesolimbic dopamine systems, and corticolimbic glutamate signals that interact with those systems. We focus on ways in which these brain reward circuits might participate in obesity or in eating disorders.

Dopamine receptor modulation of repetitive grooming actions in the rat: potential relevance for Tourette syndrome

Studies of rodent grooming can provide valuable insight for dopamine contributions to the initiation, organization, and repetition of motor patterns. This information is useful for understanding how brain dysfunctions contribute to movement disorders such as Tourette syndrome and obsessive compulsive disorder, in which patients are driven to reiterate particular movement patterns. In rodents, dopamine D1 receptor stimulation causes a complex behavioral super-stereotypy in the form of excessive production and rigid execution of whole sequences of movements known as syntactic grooming chains. Sequential super-stereotypy of grooming chains may be particularly advantageous for modeling movement sequences and treatments in Tourette syndrome and related disorders. Here, we report that co-administration of haloperidol, one available treatment for Tourette syndrome and primarily a D2 receptor antagonist, prevented D1 stimulation with SKF38393 from inducing sequential super-stereotypy, which manifests as an exaggeration of the tendency to complete all four phases of a syntactic chain in rigid serial order once the first phase has begun. In a separate experiment, we showed that in contrast to acute D1 agonist administration, 39h withdrawal from chronic (3weeks) administration of the D1 antagonist SCH23390 (which has been suggested to increase D1 receptor expression in the basal ganglia) did not elicit sequential super-stereotypy after drug cessation. Instead, rats suddenly removed from repeated SCH23390 spent more time performing simple stereotypies that included intense scratching and biting behaviors. Together, these results have implications for understanding how dopamine receptors facilitate particular stereotypies manifest in animal models of Tourette syndrome and obsessive compulsive disorder.

A neural computational model of incentive salience

Incentive salience is a motivational property with 'magnet-like' qualities. When attributed to reward-predicting stimuli (cues), incentive salience triggers a pulse of 'wanting' and an individual is pulled toward the cues and reward. A key computational question is how incentive salience is generated during a cue re-encounter, which combines both learning and the state of limbic brain mechanisms. Learning processes, such as temporal-difference models, provide one way for stimuli to acquire cached predictive values of rewards. However, empirical data show that subsequent incentive values are also modulated on the fly by dynamic fluctuation in physiological states, altering cached values in ways requiring additional motivation mechanisms. Dynamic modulation of incentive salience for a Pavlovian conditioned stimulus (CS or cue) occurs during certain states, without necessarily requiring (re)learning about the cue. In some cases, dynamic modulation of cue value occurs during states that are quite novel, never having been experienced before, and even prior to experience of the associated unconditioned reward in the new state. Such cases can include novel drug-induced mesolimbic activation and addictive incentive-sensitization, as well as natural appetite states such as salt appetite. Dynamic enhancement specifically raises the incentive salience of an appropriate CS, without necessarily changing that of other CSs. Here we suggest a new computational model that modulates incentive salience by integrating changing physiological states with prior learning. We support the model with behavioral and neurobiological data from empirical tests that demonstrate dynamic elevations in cue-triggered motivation (involving natural salt appetite, and drug-induced intoxication and sensitization). Our data call for a dynamic model of incentive salience, such as presented here. Computational models can adequately capture fluctuations in cue-triggered 'wanting' only by incorporating modulation of previously learned values by natural appetite and addiction-related states.

'Liking' and 'wanting' food rewards: brain substrates and roles in eating disorders

What brain reward systems mediate motivational 'wanting' and hedonic 'liking' for food rewards? And what roles do those systems play in eating disorders? This article surveys recent findings regarding brain mechanisms of hedonic 'liking', such as the existence of cubic-millimeter hedonic hotspots in nucleus accumbens and ventral pallidum for opioid amplification of sensory pleasure. It also considers brain 'wanting' or incentive salience systems important to appetite, such as mesolimbic dopamine systems and opioid motivation circuits that extend beyond the hedonic hotspots. Finally, it considers some potential ways in which 'wanting' and 'liking' might relate to eating disorders.

Affective neuroscience of pleasure: reward in humans and animals

INTRODUCTION

Pleasure and reward are generated by brain circuits that are largely shared between humans and other animals.

DISCUSSION

Here, we survey some fundamental topics regarding pleasure mechanisms and explicitly compare humans and animals.

CONCLUSION

Topics surveyed include liking, wanting, and learning components of reward; brain coding versus brain causing of reward; subjective pleasure versus objective hedonic reactions; roles of orbitofrontal cortex and related cortex regions; subcortical hedonic hotspots for pleasure generation; reappraisals of dopamine and pleasure-electrode controversies; and the relation of pleasure to happiness.

Measurement of rodent stereotyped behavior

This unit presents a quantitative, observational method for the assessment of rodent stereotyped behavior which consists of motor responses that are repetitive, invariant, and seemingly without purpose or goal. The most classic behavioral pattern that is characteristic of stereotypy is that elicited by high doses of stimulants, such as cocaine and amphetamine, in rats, although it can also occur in response to other drugs or neurotoxic treatments affecting the basal ganglia. An observational time-sampling procedure is described in which animals are observed and rated by an experimenter, who is blind to treatment, at regular time points over the course of a behavioral testing period. The frequency of different behaviors is measured by scoring the presence or absence of a given behavior during predetermined time bins. The apparatus and test procedures are described, and a comprehensive list of commonly observed behaviors that may appear as stereotyped is provided. In addition to being ideally suited to the measurement of stereotypy, the protocol can be adapted to sampling many forms of spontaneous behaviors, including locomotion, rearing, grooming, eating, and drinking. Samples of behavioral checklists and scoring sheets are also provided.

The problem of serial order in behavior: Lashley’s legacy

In a prescient paper Karl Lashley (1951) rejected reflex chaining accounts of the sequencing of behavior and argued instead for a more cognitive account in which behavioral sequences are typically controlled with central plans. An important feature of such plans, according to Lashley, is that they are hierarchical. Lashley offered several sources of evidence for the hierarchical organization for behavioral plans, and others afterward provided more evidence for this hypothesis. We briefly review that evidence here and then shift from a focus on the structure of plans (Lashley's point of concentration) to the processes by which plans are formed in real time. Two principles emerge from the studies we review. One is that plans are not formed from scratch for each successive movement sequence but instead are formed by making whatever changes are needed to distinguish the movement sequence to be performed next from the movement sequence that has just been performed. This plan-modification view is supported by two phenomena discovered in our laboratory: the parameter remapping effect, and the handpath priming effect. The other principle we review is that even single movements appear to be controlled with hierarchically organized plans. At the top level are the starting and goal postures. At the lower level are the intermediate states comprising the transition from the starting posture to the goal posture. The latter principle is supported by another phenomenon discovered in our lab, the end-state comfort effect, and by a computational model of motor planning which accounts for a large number of motor phenomena. Interestingly, the computational model hearkens back to a classical method of generating cartoon animations that relies on the production of keyframes first and the production of interframes (intermediate frames) second.

Behavioral electrophysiology of psychostimulants

The motor-activating effects of amphetamine and other psychostimulants such as cocaine depend on an increase in dopamine (DA) transmission in the striatum, a key component of the basal ganglia and the forebrain motive circuit. This review focuses on research aimed at using electrophysiological techniques--including extracellular unit recording and iontophoresis--in alert, fully functioning animals to understand how these drugs alter striatal neuronal processing under behaviorally relevant conditions. The data indicate that DA works in conjunction with glutamate (GLU), an excitatory amino acid, to enhance the signal-to-noise ratio of afferent information. This DA-GLU interaction appears to play a critical role in the amphetamine-induced activation of striatal neurons. The pattern of striatal activation, moreover, changes as the behavioral response changes from unfocused locomotion to highly focused, stereotyped behavior, but interestingly, the striatal response pattern is not reflected in substantia nigra reticulata, a primary target of striatal efferents. Although cocaine also activates striatal neurons during behavior, the underlying mechanisms appear to be complicated by factors unique to this drug and deserve further evaluation. Collectively, these findings provide unique insight into the neuronal processes by which the striatum participates in psychostimulant-induced motor behavior.

Neuroanatomical localization of an internal clock: A functional link between mesolimbic, nigrostriatal, and mesocortical dopaminergic systems

The effects of selective dopamine (DA) depleting lesions with 6-hydroxydopamine microinjection into the SN, CPu, and NAS, as well as radiofrequency lesions of the CPu on the performance characteristics of rats trained on a single-valued 20-s peak-interval (PI) timing procedure or a double-valued 10-s and 60-s PI procedure were evaluated. A double dissociation in the performance of duration discriminations was found. Rats with CPu lesions were unable to exhibit temporal control of their behavior suggesting complete insensitivity to signal duration but were able to show discrimination of the relative reward value of a signal by differentially modifying their response rates appropriately. In contrast, rats with NAS lesions were able to exhibit temporal control of their behavior by differentially modifying their response rates as a function of signal duration(s), suggesting no impairment of sensitivity to signal duration, but were unable to show discrimination of the relative reward value of a signal.

Behavioral and histological characterization of unilateral cervical spinal cord contusion injury in rats

Most experimental studies of spinal cord injury (SCI) in rats damage the thoracic cord, with the consequent functional loss being due to interruption of long tracts connecting the caudal spinal cord to the rostral nervous system. Less work has been done evaluating injury to the cervical cord, even though it is the most common level of human SCI. In addition to the long tracts, the cervical spinal cord contains the sensory and motor neurons responsible for upper extremity function. The purpose of this study was to further develop a rat model of cervical spinal cord contusion injury using a modified NYU/MASCIS weight drop device. Mild (6.25 mm) and moderate (12.5 mm) C5 unilateral injuries were produced. Behavioral recovery was examined using a grooming test, a paw preference test, a walkway test (The Catwalk), and a horizontal ladder test. Histological outcome measures included sparing at the lesion epicenter, sparing throughout the extent of the lesion, quantification of myelin loss rostral and caudal to the lesion, and motor neuron counts. Compared to controls, animals receiving SCI exhibited injury severity-specific deficits in forelimb, locomotor, and hindlimb function persisting for 6-weeks post-SCI. Histological analysis revealed ipsilateral containment of the injury, and differentiation between groups on all measures except motor neuron counts. This model has many advantages: (1) minimal animal care requirements post-SCI, (2) within subject controls, (3) functional loss involves primarily the ipsilateral forelimb, and (4) it is a behavioral and histological model for both gray and white matter damage caused by contusive SCI.

Regional cerebral perfusion abnormalities in developmental language disorder. Statistical parametric mapping analysis

OBJECTIVE

A voxel based investigation of cerebral blood flow was conducted to identify brain functional differences during resting state between children with developmental language disorder (DLD) and normal controls.

METHOD

Using DSM-IV criteria, we selected 21 children with DLD. All children were examined by technetium-99m-HMPAO Brain SPECT. Using SPM analyses, we compared the SPECT images of children with DLD and those of 17 control subjects on a voxel by voxel basis using ANCOVA covarying for age.

RESULTS

Reduced cerebral blood flow in the right putamen,the right inferior parietal cortex, and the left globus pallidus were found in children with DLD versus the controls. However, no area of increased cerebral blood flow was observed in children with DLD compared to the controls.

CONCLUSION

Though results should be interpreted cautiously, this study confirms the presence of functional defects in the basal ganglia and the inferior parietal lobe during the resting state of the brains of children with DLD. It also gives further evidence for functional deficits in basal ganglia as an important factor in the etiology of DLD.

Neurons in hippocampal afferent zones of rat striatum parse routes into multi-pace segments during maze navigation

Hippocampal 'place' neurons discharge when rats occupy specific regions within an environment. This finding is a cornerstone of the theory of the hippocampus as a cognitive map of space. But for navigation, representations of current position must be implemented by signals concerning where to go next, and how to get there. In recordings in hippocampal output structures associated with the motor system (nucleus accumbens and ventromedial caudate nucleus) in rats solving a plus-maze, neurons fired continuously from the moment the rat left one location until it arrived at the next goal site, or at an intermediate place, such as the maze centre. While other studies have shown discharges during reward approach behaviours, this is the first demonstration of activity corresponding to the parsing of complex routes into sequences of movements between landmarks, similar to the lists of instructions we often employ to communicate directions to follow between points on a map. As these cells fired during a series of several paces or re-orientation movements, perhaps this is homologous to 'chunking'. The temporal overlaps in the activity profiles of the individual neurons provide a possible substrate to successively trigger movements required to arrive at the goal. These hippocampally informed, and in some cases, spatially selective responses support the view of the ventral striatum as an interface between limbic and motor systems, permitting contextual representations to have an impact on fundamental action sequences for goal-directed behaviour.

On the nature and evolution of the neural bases of human language

The traditional theory equating the brain bases of language with Broca's and Wernicke's neocortical areas is wrong. Neural circuits linking activity in anatomically segregated populations of neurons in subcortical structures and the neocortex throughout the human brain regulate complex behaviors such as walking, talking, and comprehending the meaning of sentences. When we hear or read a word, neural structures involved in the perception or real-world associations of the word are activated as well as posterior cortical regions adjacent to Wernicke's area. Many areas of the neocortex and subcortical structures support the cortical-striatal-cortical circuits that confer complex syntactic ability, speech production, and a large vocabulary. However, many of these structures also form part of the neural circuits regulating other aspects of behavior. For example, the basal ganglia, which regulate motor control, are also crucial elements in the circuits that confer human linguistic ability and abstract reasoning. The cerebellum, traditionally associated with motor control, is active in motor learning. The basal ganglia are also key elements in reward-based learning. Data from studies of Broca's aphasia, Parkinson's disease, hypoxia, focal brain damage, and a genetically transmitted brain anomaly (the putative "language gene," family KE), and from comparative studies of the brains and behavior of other species, demonstrate that the basal ganglia sequence the discrete elements that constitute a complete motor act, syntactic process, or thought process. Imaging studies of intact human subjects and electrophysiologic and tracer studies of the brains and behavior of other species confirm these findings. As Dobzansky put it, "Nothing in biology makes sense except in the light of evolution" (cited in Mayr, 1982). That applies with as much force to the human brain and the neural bases of language as it does to the human foot or jaw. The converse follows: the mark of evolution on the brains of human beings and other species provides insight into the evolution of the brain bases of human language. The neural substrate that regulated motor control in the common ancestor of apes and humans most likely was modified to enhance cognitive and linguistic ability. Speech communication played a central role in this process. However, the process that ultimately resulted in the human brain may have started when our earliest hominid ancestors began to walk.

Substantia nigra pars reticulata neurons code initiation of a serial pattern: implications for natural action sequences and sequential disorders

Sequences of movements are initiated abnormally in neurological disorders involving basal ganglia dysfunction, such as Parkinson's disease or Tourette's syndrome. The substantia nigra pars reticulata (SNpr) is one of the two primary output structures of the basal ganglia. However, little is known about how substantia nigra mediates the initiation of normal movement sequences. We studied its role in coding initiation of a sequentially stereotyped but natural movement sequence by recording neuronal activity in SNpr during behavioural performance of 'syntactic grooming chains'. These are rule-governed sequences of up to 25 grooming movements emitted in four predictable (syntactic) phases, which occur spontaneously during grooming behaviour by rats and other rodents. Our results show that neuronal activation in central SNpr codes the onset of this entire rule-governed sequential pattern of grooming actions, not elemental grooming movements. We conclude that the context of sequential pattern may be more important than the elemental motor parameters in determining SNpr neuronal activation.

Hoxb8 is required for normal grooming behavior in mice

Repertoires of grooming behaviors critical to survival are exhibited by most animal species, including humans. Genes that influence this complex behavior are unknown. We report that mice with disruptions of Hoxb8 show, with 100% penetrance, excessive grooming leading to hair removal and lesions. Additionally, these mice excessively groom normal cagemates. We have been unable to detect any skin or PNS abnormalities in Hoxb8 mutants. These observations suggest that the excessive, pathological grooming exhibited by these mice results from CNS abnormalities. Consistent with this interpretation, we demonstrate Hoxb8 expression in regions of the adult mouse CNS previously implicated in the control of grooming. The aberrant behavior observed in Hoxb8 mutants is not unlike that of humans suffering from the OC-spectrum disorder, trichotillomania. Interestingly, Hoxb8 is expressed in regions of the CNS known as the "OCD-circuit."

Influence of cholinergic system on motor learning during aging in mice

Three, 12- and 20-month-old C57Bl6 mice, reared in standard conditions or in an enriched environment, were administered subcutaneously either scopolamine hydrobromide (SIGMA), 0.6 and 1.2 mg kg(-1), or physiological saline 15 min before testing their motor skills (muscular strength, dynamic equilibrium and motor coordination) and motor learning abilities (number of trials needed to reach a learning criterion on a rotorod rotating at 27 revolutions per min). The results demonstrated a lack of correlation between motor skill scores and between motor skill and motor learning scores, suggesting that the rotorod training procedure measures motor learning and not motor skills or is insensitive to changes in motor skills. They also demonstrated that motor skills decreased with age but were insensitive to environmental rearing and to scopolamine. In contrast, the learning scores, which also decreased with age, were very sensitive to scopolamine, particularly in the oldest mice. These results are discussed according to the role of cholinergic system in motor learning during aging.

Super-stereotypy I: enhancement of a complex movement sequence by systemic dopamine D1 agonists

Peripheral administration of D1 dopamine agonists elicits grooming behavior from rodents. The present study examined grooming behavior and the relative probability and stereotypy of a natural sequence of grooming movements (called a syntactic grooming chain) that follows a predictable fixed pattern of serial order. We compared the amount of grooming behavior vs. the stereotypy of sequential patterns after peripheral administration of either a partial D1 agonist (SKF 38393; 2.5, 5.0, 10, 20 mg/kg), a full D1 agonist (SKF 82958; 0.1, 0.2, 0.5, 1.0 mg/kg; i.p.), a D2 agonist (quinpirole; 5.0, 10 mg/kg), or ACTH (2.0, 5.0 mg/kg). There was a dissociation between the elicited grooming amount, the pattern frequency, and the pattern completion or sequential stereotypy after these drugs. Quinpirole and ACTH both reduced the likelihood that the sequential pattern would be completed in the normal pattern (and reduced the overall amount of grooming). Administration of either SKF 38393 or SKF 82958 increased the tendency to engage in complex stereotyped sequential patterns of grooming (even though only the partial D1 agonist increased the total amount of grooming). In addition, SKF 38393 increased the sequential stereotypy of the already-stereotyped pattern itself (as measured by the probability of completing the stereotyped sequence once it began). Thus, dopamine D1 receptor activation appears to contribute to a kind of sequential super-stereotypy in which a complex, stereotyped behavioral sequence is initiated more frequently and more often goes to completion.

Do California ground squirrels (Spermophilus beecheyi) use ritualized syntactic cephalocaudal grooming as an agonistic signal?

Animal communication theory holds that many signals have evolved from nonsignal precursors. This field and laboratory study of California ground squirrels (Spermophilus beecheyi) provides evidence for the coexistence of such a precursor with its derived display. The precursor is an ancient, endogenously sequenced (syntactic) pattern of cephalocaudal grooming movements (CCGs) shared by all rodent suborders. The following evidence supports the hypothesis that a supernormal version of this pattern has been selected for signal function. Syntactic CCGs in the field (a) were more rigidly stereotyped than ordinary syntactic CCGs in the laboratory; (b) differed from laboratory syntactic CCGs in other ways that enhanced their conspicuousness, in part through exaggeration of the syntactic cephalocaudal pattern; (c) were associated with scent marking and social staring; and (d) were associated with intrasexual agonistic encounters that did not escalate to fighting.

Super-stereotypy II: enhancement of a complex movement sequence by intraventricular dopamine D1 agonists

This study compared the effect of intraventricular administration of dopamine D1 or D2 agonists or of ACTH on the sequential stereotypy of a serial pattern of grooming movements ("syntactic chain"). In a previous study, we showed that peripheral administration of D1 agonists increased the probability of occurrence and enhanced the stereotypy of the already-stereotyped movement pattern. Here we made microinjections of either SKF 38393 (a partial D1 agonist; 5, 10, 15, 20, 40 microg), SKF 82958 (a full D1 agonist; 5, 10, 20 microg), quinpirole (a D2 agonist; 5, 10, 20 microg), or ACTH-(1-24) (2, 5, 10 microg) into the lateral ventricles of rats. We measured the amount of grooming, the relative probability that the complex sequence pattern would occur, and the degree to which the syntactic pattern was completed faithfully. The total amount of grooming behavior was increased by intraventricular SKF 82958 and by ACTH, but was not changed by SKF 38393 and was decreased by quinpirole. Super-stereotypy of the sequential pattern was produced only by dopamine D1 agonists. The relative probability of initiating the syntactical sequence was increased by both SKF 38393 and SKF 82958, but was reduced by quinpirole and ACTH. The full D1 agonist, SKF 82958, also increased the likelihood that the pattern would be completed, thus causing sequential super-stereotypy in the strongest sense. Our results highlight a role for dopamine D1 receptors, probably within the basal ganglia, in the production of sequential super-stereotypy of complex behavioral patterns.

The effect of callosotomy on novel versus familiar bimanual actions: a neural dissociation between controlled and automatic processes?

The corpus collosum is the large band of fibers that connects the two cerebral hemispheres of the brain. Individuals who have had the fibers of these tracts surgically severed by callosotomy are able to draw two different spatial figures simultaneously using the left and right hands, without evidence of interactions in the spatial planning processes. Paradoxically, tasks (e.g., tying shoes) that appear to depend on spatial interactions between the left and right hands, each of which is controlled by a separate cerebral hemisphere, pose little difficulty. How can this be? In the study reported here, we observed that well-learned cooperative actions of the hands remain intact in 2 callosotomy patients, whereas actions novel to these patients are virtually impossible for them to produce without visual guidance. We infer that duplicate memory engrams of well-learned actions can be accessed by both cerebral hemispheres without callosal mediation, whereas callosal interactions are necessary for precise cross-matching of sensory information during spatial planning or perceptual-motor learning.

Dopamine and the origins of human intelligence

A general theory is proposed that attributes the origins of human intelligence to an expansion of dopaminergic systems in human cognition. Dopamine is postulated to be the key neurotransmitter regulating six predominantly left-hemispheric cognitive skills critical to human language and thought: motor planning, working memory, cognitive flexibility, abstract reasoning, temporal analysis/sequencing, and generativity. A dopaminergic expansion during early hominid evolution could have enabled successful chase-hunting in the savannas of sub-Saharan Africa, given the critical role of dopamine in counteracting hyperthermia during endurance activity. In turn, changes in physical activity and diet may have further increased cortical dopamine levels by augmenting tyrosine and its conversion to dopamine in the central nervous system (CNS). By means of the regulatory action of dopamine and other substances, the physiological and dietary changes may have contributed to the vertical elongation of the body, increased brain size, and increased cortical convolutedness that occurred during human evolution. Finally, emphasizing the role of dopamine in human intelligence may offer a new perspective on the advanced cognitive reasoning skills in nonprimate lineages such as cetaceans and avians, whose cortical anatomy differs radically from that of primates.

Behavior-related changes in the activity of substantia nigra pars reticulata neurons in freely moving rats

As one of the primary targets of the striatum, the substantia nigra pars reticulata (SNr) has been hypothesized to play a role in normal motor behavior. Specifically, inhibition of usually high, tonic SNr output is predicted to correlate with motor activation. While support for this has come primarily from electrophysiological studies in primates performing goal-directed movements, we tested this hypothesis in rats behaving in an open-field arena. SNr single-unit activity was recorded during spontaneous bouts of open-field behavior (e.g., head and body movements, locomotion) and after rats were given D-amphetamine (1.0 mg/kg, s.c.), which reliably increases motor activity and elevates the firing of motor-related striatal neurons. Prior to drug administration, SNr neurons had either regular, slightly irregular or irregular firing patterns when animals rested quietly. During movement, some inhibitions were observed, but the majority ( approximately 79%) of analyzed units increased firing by as much as 38%. Regardless of the predrug behavioral response of the cell, amphetamine strongly inhibited firing rate ( approximately 90% below nonmovement baseline) and changed firing pattern such that all cells fired irregularly. Subsequent injection with the dopamine antagonist haloperidol (1.0 mg/kg, s.c.) reversed amphetamine-induced inhibitions in all tested cells, which supports a role for dopamine in this effect. These results suggest that the pattern of striatal activity established by amphetamine, which may be critical for determining the drug-induced behavioral pattern, is represented in the SNr regardless of the predrug behavioral response of the cell.

Effects of electrolytic lesions of the lateral pallidum on motor coordination, spatial learning, and regional brain variations of cytochrome oxidase activity in rats

In view of recent theories suggesting a role for basal ganglia circuits in motor control and cognition, rats with bilateral electrolytic lesions of the lateral part of the globus pallidus were compared with control rats on motor coordination tasks and spatial learning in the Morris water maze. By comparison with sham-operated controls, rats with lesions of the lateral pallidum were impaired during acquisition of the rotorod task. Deficits were observed in a wooden beam task, but not in hole-board and suspended string tests. In addition, lesioned rats were impaired during acquisition of place learning but not of visuomotor guidance in the Morris water maze. Alterations of brain metabolism, as assessed by cytochrome oxidase activity, were found in three regions of lesioned rats, the subthalamic nucleus, the superior colliculus, and the centromedial thalamus of lesioned rats, probably as a result of interrupted neocortico-basal ganglia circuitry as a secondary consequence of the primary lesion.

Ascorbate modulates glutamate-induced excitations of striatal neurons

To assess the role of ascorbate (AA), an antioxidant vitamin, in modulating striatal activity, single-unit recording was combined with iontophoresis in awake, unrestrained rats. Brief applications of AA (20 s, 5-80 nA) elicited few changes in either basal activity or activity evoked by continuous application of glutamate (GLU), but relatively high AA ejection currents (>40 nA) often inhibited fast-firing units. Comparable results were obtained with the antioxidant isomer, iso-AA, suggesting the AA-induced inhibition represents a high-dose, antioxidant effect. When applied for prolonged periods (2-4 min) at doses that failed to alter basal activity, AA either enhanced or attenuated the excitatory response to test pulses of GLU. The AA-induced enhancement occurred more frequently (16 vs. 6 applications) and was characterized by a more rapid (shorter onset and peak latencies) and more pronounced (greater peak magnitude) excitation to GLU without an evident change in offset latency. In most cases, further increases in AA ejection current attenuated the GLU response. Iso-AA, in contrast, had only inhibitory effects, which occurred at moderate- to high-dose applications. Collectively, these results suggest that AA, apart from its antioxidant effects, modulates phasic changes in striatal excitability induced by GLU. Because extracellular levels of striatal AA fluctuate in relation to behavioral activation, this neuromodulatory action of AA may contribute to behaviorally relevant changes in sensorimotor responsivity.

Cocaine-induced activation of striatal neurons during focused stereotypy in rats

As psychomotor stimulants, both amphetamine and cocaine elicit episodes of repetitive motor activation (focused stereotypy) known to involve the mesostriatal dopamine system. During amphetamine-induced focused stereotypy, motor-related neurons in the striatum respond with either an excitation or inhibition, depending on dose and behavioral pattern, whereas nonmotor-related units are inhibited. To assess striatal activity during the focused stereotypy induced by cocaine, both types of striatal units were recorded in ambulant rats. Either 20 or 40 mg/kg cocaine caused highly focused sniffing and head bobbing, which occurred in conjunction with activation of both motor- and nonmotor-related neurons. The activation of motor-related units was evident even when firing rate was compared during periods of matched pre- and post-drug behavior, arguing against movement as the sole basis for the drug-induced neuronal excitation. Subsequent administration of haloperidol (1.0 mg/kg) reversed but did not completely block the neuronal activation, while the behavioral response shifted away from focused stereotypy toward an increase in ambulation. Thus, the level of activation of both motor- and nonmotor-related striatal neurons may play a critical role in the behavioral response pattern induced by cocaine.

Action sequencing is impaired in D1A-deficient mutant mice

The role of dopamine in the production of behaviour is multifarious in that it can influence different aspects of movement (e.g. movement initiation, sensorimotor integration, and movement sequencing). A characteristic of the dopamine system which seems to be critical for the expression of this diverse influence is its varied receptor population. Previous studies have shown that specific receptor subtype activation leads to specific behavioural responses or alterations of selective aspects of movement. It is known that one of the important influences of dopamine includes sequential co-ordination of 'syntactic' patterns of grooming movements because moderate loss of the dopaminergic nigrostriatal projections specifically disrupts these patterns without affecting grooming actions in a general fashion (Berridge, K.C. Psychobiology, 15, 336, 1989). The specific receptors of the dopamine family which play a key part in this co-ordination of movement sequences is not known. In the present study, we examined the serial order of particular syntactic sequences or chains of grooming actions in mice lacking D1A receptors to explore the relationship between this receptor subtype and movement sequencing. Mutant mice had shorter grooming bouts and a disruption of the organization of sequential patterns compared with wild-type littermate controls. Sequential disruption was reflected in the failure of D1A mutants to follow the syntactic pattern of grooming to completion. This sequential disruption deficit appeared to be specific, as mutant mice initiated more syntactic chains than wild-type controls even though they were less likely to complete them. These results support the hypothesis that D1A receptor activation plays a part in the sequencing of natural action. This conclusion has important implications for the understanding of the functional heterogeneity of dopamine receptor subtypes and of the aetiology of symptoms observed in patients with basal ganglia disease.

Real-time assessments of dopamine function during behavior: single-unit recording, iontophoresis, and fast-scan cyclic voltammetry in awake, unrestrained rats

Although ample evidence implicates the dopamine (DA) projection to the neostriatum and nucleus accumbens in motor and motivational processes, relatively little information is available on how DA alters neostriatal or accumbal functions under naturally occurring behavioral conditions. Further insight into neuron-behavior relationships can be achieved with the application of single-unit recording techniques, including iontophoresis and fast-scan cyclic voltammetry (FSCV), to awake, unrestrained animals. Single-unit recording has revealed that amphetamine, a widely abused psychomotor stimulant, activates motor-, but inhibits nonmotor-related neurons in neostriatum and nucleus accumbens. Although either response can be blocked by DA receptor antagonists, the amphetamine-induced activation also depends on an intact corticostriatal system, suggesting a role for glutamate (GLU). Both neostriatal and accumbal neurons are sensitive to iontophoretic application of either DA or GLU, but when applied during low-dose application of DA, the GLU signal is enhanced relative to background activity. In effect, DA appears to modulate GLU by strengthening the GLU signal-to-noise ratio. To assess DA release under behaviorally relevant conditions, FSCV has been used to obtain real-time measurements of DA efflux in a free-choice novelty test. DA efflux increased only during the brief period of entry into novelty, and the increase was confined to accumbal shell and the shell-core transition zone, the so-called shore. Neither accumbal core nor the overlying neostriatum showed a novelty-related DA change. Thus, DA release during behavior is not uniform and in the case of novelty appears targeted to the limbic-related area of accumbal shell. Further application of these and other in vivo technologies to ambulant animals is required to identify the complex mechanisms underlying both the release of DA and its effect on neostriatal and accumbal neurons during behavior.

Selective speech motor, syntax and cognitive deficits associated with bilateral damage to the putamen and the head of the caudate nucleus: a case study

Deficits in speech production, sentence comprehension and abstract reasoning occurred in a subject having profound bilateral damage to the putamen and the caudate nucleus. Acoustic analyses indicated that the subject's speech was degraded due to inappropriate sequencing of articulatory gestures that involve different articulatory structures. Transitions between sounds were slow and often did not achieve target configurations. The subject had a 14% error rate comprehending distinctions in meaning conveyed by syntax in English sentences; normal controls make virtually no errors in this test. Cognitive deficits involving impaired sequencing occurred: the subject had a 70% error rate on the Odd Man Out test when making decisions within a single category. Cognitive perseveration occurred when the subject was asked to shift categories. In contrast, performance was within normal ranges in tests of lexical access and memory. The pattern of deficits provides evidence for basal ganglia involvement in the regulation of sequencing across modalities.

Iontophoresis of amphetamine in the neostriatum and nucleus accumbens of awake, unrestrained rats

When administered systemically to ambulant animals, amphetamine (AMPH) has both excitatory and inhibitory effects on single-unit activity in the neostriatum and nucleus accumbens. To determine the extent to which these results reflect a direct action of the drug, AMPH was applied iontophoretically to neostriatal and accumbal neurons under naturally occurring behavioral conditions. AMPH dose-dependently (5-40 nA) inhibited the vast majority of spontaneously active units. The inhibition, which was evident at low ejection currents (5-10 nA), had relatively short onset (4-12 s) and offset (6-24 s) latencies, and was positively correlated with basal firing rate. Even stronger dose-dependent inhibitory responses were recorded when neurons having no or a very low rate of spontaneous activity were tonically activated by continuous, low-current applications of glutamate (Glu). Systemic injection of either SCH-23390 (0.1 mg/kg) or haloperidol (0.2 mg/kg), relatively selective D1 and D2 receptor antagonists, respectively, blocked the AMPH-induced inhibition. Prolonged AMPH iontophoresis (2-3 min; 5-30 nA) inhibited both spontaneous impulse activity and Glu-induced excitations, resulting in a complete blockade of the Glu response at relatively high AMPH ejection currents (> or = 20 nA). Taken together, these results suggest that although dopamine is largely responsible for the inhibitory effects of iontophoretic AMPH, dopamine alone cannot account for the complex response of neostriatal and accumbal neurons to systemic AMPH administration.

Sex differences in the effect of amphetamine on immediate early gene expression in the rat dorsal striatum

Amphetamine (AMPH)-induced dopamine release in the striatum and AMPH-induced behavior in the rat have been demonstrated to be influenced by sex and hormonal status. The experiments reported here were conducted, therefore, to examine sex differences, hormonal influences and estrous cycle-dependent changes in AMPH-induced immediate early gene expression in the dorsal striatum. Cell counts were taken at three rostrocaudal levels from three to four regions of the dorsal striatum at each level (ventromedial, dorsomedial, dorsolateral, ventrolateral). The immunohistochemical localization of calbindin was used as a control. We report here that females on the afternoon of proestrus had a significantly greater percent of Fos-positive neurons after AMPH across the dorsolateral region of the middle and caudal striatum and in the ventrolateral region of the caudal striatum compared to females in diestrus, ovariectomized (OVX) females, castrated (CAST) males and intact males. There was no difference in AMPH-induced immediate early gene expression between OVX and diestrous rats. There were also no significant differences between CAST and intact males in AMPH-induced Fos expression, with the exception of the ventrolateral caudal striatum. In sum, the present findings indicate that AMPH-induced Fos expression is sexually dimorphic and modulated by gonadal hormones in lateral regions of the rat dorsal striatum.