Mapping brain networks in awake mice using combined optical neural control and fMRI.

Behaviors and brain disorders involve neural circuits that are widely distributed in the brain. The ability to map the functional connectivity of distributed circuits, and to assess how this connectivity evolves over time, will be facilitated by methods for characterizing the network impact of activating a specific subcircuit, cell type, or projection pathway. We describe here an approach using high-resolution blood oxygenation level-dependent (BOLD) functional MRI (fMRI) of the awake mouse brain-to measure the distributed BOLD response evoked by optical activation of a local, defined cell class expressing the light-gated ion channel channelrhodopsin-2 (ChR2). The utility of this opto-fMRI approach was explored by identifying known cortical and subcortical targets of pyramidal cells of the primary somatosensory cortex (SI) and by analyzing how the set of regions recruited by optogenetically driven SI activity differs between the awake and anesthetized states. Results showed positive BOLD responses in a distributed network that included secondary somatosensory cortex (SII), primary motor cortex (MI), caudoputamen (CP), and contralateral SI (c-SI). Measures in awake compared with anesthetized mice (0.7% isoflurane) showed significantly increased BOLD response in the local region (SI) and indirectly stimulated regions (SII, MI, CP, and c-SI), as well as increased BOLD signal temporal correlations between pairs of regions. These collective results suggest opto-fMRI can provide a controlled means for characterizing the distributed network downstream of a defined cell class in the awake brain. Opto-fMRI may find use in examining causal links between defined circuit elements in diverse behaviors and pathologies.

Dopamine and beta-band oscillations differentially link to striatal value and motor control.

Parkinson's disease is characterized by decreased dopamine and increased beta-band oscillatory activity accompanying debilitating motor and mood impairments. Coordinate dopamine-beta opposition is considered a normative rule for basal ganglia function. We report a breakdown of this rule. We developed multimodal systems allowing the first simultaneous, chronic recordings of dopamine release and beta-band activity in the striatum of nonhuman primates during behavioral performance. Dopamine and beta signals were anticorrelated over seconds-long time frames, in agreement with the posited rule, but at finer time scales, we identified conditions in which these signals were modulated with the same polarity. These measurements demonstrated that task-elicited beta suppressions preceded dopamine peaks and that relative dopamine-beta timing and polarity depended on reward value, performance history, movement, and striatal domain. These findings establish a new view of coordinate dopamine and beta signaling operations, critical to guide novel strategies for diagnosing and treating Parkinson's disease and related neurodegenerative disorders.

Characterizing learning by simultaneous analysis of continuous and binary measures of performance.

Continuous observations, such as reaction and run times, and binary observations, such as correct/incorrect responses, are recorded routinely in behavioral learning experiments. Although both types of performance measures are often recorded simultaneously, the two have not been used in combination to evaluate learning. We present a state-space model of learning in which the observation process has simultaneously recorded continuous and binary measures of performance. We use these performance measures simultaneously to estimate the model parameters and the unobserved cognitive state process by maximum likelihood using an approximate expectation maximization (EM) algorithm. We introduce the concept of a reaction-time curve and reformulate our previous definitions of the learning curve, the ideal observer curve, the learning trial and between-trial comparisons of performance in terms of the new model. We illustrate the properties of the new model in an analysis of a simulated learning experiment. In the simulated data analysis, simultaneous use of the two measures of performance provided more credible and accurate estimates of the learning than either measure analyzed separately. We also analyze two actual learning experiments in which the performance of rats and of monkeys was tracked across trials by simultaneously recorded reaction and run times and the correct and incorrect responses. In the analysis of the actual experiments, our algorithm gave a straightforward, efficient way to characterize learning by combining continuous and binary measures of performance. This analysis paradigm has implications for characterizing learning and for the more general problem of combining different data types to characterize the properties of a neural system.

Effect of the nigrostriatal dopamine system on acquired neural responses in the striatum of behaving monkeys.

Dysfunction of the nigrostriatal dopamine system results in marked disorders of movement such as occur in Parkinson's disease. Functions of this dopamine-containing projection system were examined in monkeys trained in a classical conditioning task, and the effects of striatal dopamine depletion were tested. Unilateral dopamine loss substantially reduced the acquired sensory responsiveness of striatal neurons monitored electrophysiologically. This effect was ipsilateral and selective, and could be reversed by apomorphine. These results suggest that the primate nigrostriatal system modulates expression of neuronal response plasticity in the striatum during sensorimotor learning.

The basal ganglia and adaptive motor control.

The basal ganglia are neural structures within the motor and cognitive control circuits in the mammalian forebrain and are interconnected with the neocortex by multiple loops. Dysfunction in these parallel loops caused by damage to the striatum results in major defects in voluntary movement, exemplified in Parkinson's disease and Huntington's disease. These parallel loops have a distributed modular architecture resembling local expert architectures of computational learning models. During sensorimotor learning, such distributed networks may be coordinated by widely spaced striatal interneurons that acquire response properties on the basis of experienced reward.

Building neural representations of habits.

Memories for habits and skills ("implicit or procedural memory") and memories for facts ("explicit or episodic memory") are built up in different brain systems and are vulnerable to different neurodegenerative disorders in humans. So that the striatum-based mechanisms underlying habit formation could be studied, chronic recordings from ensembles of striatal neurons were made with multiple tetrodes as rats learned a T-maze procedural task. Large and widely distributed changes in the neuronal activity patterns occurred in the sensorimotor striatum during behavioral acquisition, culminating in task-related activity emphasizing the beginning and end of the automatized procedure. The new ensemble patterns remained stable during weeks of subsequent performance of the same task. These results suggest that the encoding of action in the sensorimotor striatum undergoes dynamic reorganization as habit learning proceeds.

A family of cAMP-binding proteins that directly activate Rap1.

cAMP (3',5' cyclic adenosine monophosphate) is a second messenger that in eukaryotic cells induces physiological responses ranging from growth, differentiation, and gene expression to secretion and neurotransmission. Most of these effects have been attributed to the binding of cAMP to cAMP-dependent protein kinase A (PKA). Here, a family of cAMP-binding proteins that are differentially distributed in the mammalian brain and body organs and that exhibit both cAMP-binding and guanine nucleotide exchange factor (GEF) domains is reported. These cAMP-regulated GEFs (cAMP-GEFs) bind cAMP and selectively activate the Ras superfamily guanine nucleotide binding protein Rap1A in a cAMP-dependent but PKA-independent manner. Our findings suggest the need to reformulate concepts of cAMP-mediated signaling to include direct coupling to Ras superfamily signaling.

Spatiotemporal dynamics of CREB phosphorylation: transient versus sustained phosphorylation in the developing striatum.

The cAMP response element-binding protein (CREB) is a plasticity-associated transcription factor that can potentially integrate cAMP and calcium signals at the gene activation level. We tested for convergent Ser-133 phosphorylation of CREB via dopamine D1/D5 receptors and L-type calcium channels in organotypic cultures of neonatal striatum. We found such convergence only transiently. Sustained CREB phosphorylation by D1/D5 receptor and L-type channel agonists was targeted to opposite (striosome and matrix) cellular phenotypes. Subsequent expression of the CRE-containing gene, c-fos, matched the divergent patterns of sustained CREB phosphorylation, and both divergent patterns could be switched by inhibition of phosphatases, including calcineurin. Control of the duration of CREB phosphorylation may be a critical regulator of CRE-mediated gene expression by dopamine and calcium.

Network-level changes in expression of inducible Fos-Jun proteins in the striatum during chronic cocaine treatment and withdrawal.

Repeated exposure to psychomotor stimulants produce long-term changes in behavior ranging from addiction to behavioral sensitization. Many of these behaviors depend on the nigrostriatal system of the basal ganglia. We show here that chronic cocaine exposure not only leads to time-varying alterations in the inducibility of bZIP transcription factors in individual striatal neurons, but also to long-lasting network changes in which ensembles of striatal neurons express these proteins. These network-level adaptations suggest that the behavioral sensitization induced by repeated psychomotor stimulant exposure may reflect an enduring functional reorganization of basal ganglia circuits.

Dopamine D3 receptor mutant mice exhibit increased behavioral sensitivity to concurrent stimulation of D1 and D2 receptors.

The dopamine D3 receptor is expressed primarily in regions of the brain that are thought to influence motivation and motor functions. To specify in vivo D3 receptor function, we generated mutant mice lacking this receptor. Our analysis indicates that in a novel environment, D3 mutant mice are transiently more active than wild-type mice, an effect not associated with anxiety state. Moreover, D3 mutant mice exhibit enhanced behavioral sensitivity to combined injections of D1 and D2 class receptor agonists, cocaine and amphetamine. However, the combined electrophysiological effects of the same D1 and D2 agonists on single neurons within the nucleus accumbens were not altered by the D3 receptor mutation. We conclude that one function of the D3 receptor is to modulate behaviors by inhibiting the cooperative effects of postsynaptic D1 and other D2 class receptors at systems level.

A measure of striatal function predicts motor stereotypy.

To identify basal ganglia circuit dysfunctions that might produce repetitive behaviors known as motor stereotypies, we applied psychomotor stimulants and a direct dopamine receptor agonist to induce different levels of stereotypy in rats. We then used a gene induction assay to measure the functional activation of neurons in the neurochemically distinct compartments of the striatum, the striosomes and the extrastriosomal matrix. The amount by which activation in the striosomes exceeded activation in the matrix predicted the degree of motor stereotypy induced by the drug treatments. These results suggest that imbalance between compartmentally organized basal ganglia circuits may represent a neural correlate of motor stereotypy.

Neurotransmitters and neuromodulators in the basal ganglia.

The basal ganglia have become a focus for work on neurotransmitter interactions in the brain. These structures contain a remarkable diversity of neuroactive substances, organized into functional subsystems that have unique developmental histories and vulnerabilities in neurodegenerative diseases. A new view of the basal ganglia is emerging on the basis of this neurochemical heterogeneity, suggesting that dynamic regulation of transmitter expression may be a key to extrapyramidal function.

Levodopa-induced dyskinesias and dopamine-dependent stereotypies: a new hypothesis.

The basal ganglia are thought to modulate the release or inhibition of movements by way of direct and indirect pathways that act as a push-pull system of cortico-basal ganglia circuits. Here we suggest a three-pathway model of the basal ganglia that takes into consideration the fundamental division of the striatum into striosomes and extrastriosomal matrix. We suggest that, in addition to the balance between direct and indirect pathways on which normal release of individual movements depends, the balance of activity between these matrix-based pathways and the striosomal pathway regulates the frequency of release of given behavioral sequences and, thus, modulates behavioral focus. Differential plasticity in these compartmentally organized circuits might contribute to the development of L-dopa-induced dyskinesias under parkinsonian conditions and dopamine-receptor-agonist induced stereotypies under normal conditions.

Building action repertoires: memory and learning functions of the basal ganglia.

Research on the basal ganglia suggests that they are critically involved in building up sequences of behavior into meaningful, goal-directed repertoires. Work on rodents, monkeys and humans suggests that the basal ganglia act as part of a distributed forebrain system that helps to encode such repertoires through behavioral learning, and that is engaged in the expression of such repertoires once they have been internalized. The basal ganglia also may be critical to the expression of innate behavioral routines. Experimental findings on reward-based learning suggest that neural activity in the striatum and substantia nigra, pars compacta changes during behavioral learning. New evidence also suggests extreme specificity in the neural connections interrelating the basal ganglia, cerebral cortex and thalamus. Adaptive control of behavior may centrally depend on these circuits and the evaluator-reinforcement circuits that modulate them.

Basal ganglia--input, neural activity, and relation to the cortex.

In the past year new findings on the physiology and anatomy of the basal ganglia in relation to motor control systems have increased the debate about which aspects of movement control are determined at higher levels of the motor system. In addition, studies on gene regulation in the striatum have shown that behaviorally important drugs affect transmitter levels and induce changes in transcription factor expression. The cloning of dopamine receptor subtypes, and findings on neurotropic and neuroprotective effects on nigrostriatal cells, are leading to new strategies for research and clinical therapy.

Selective vulnerability of pigmented dopaminergic neurons in Parkinson's disease.

From a neuropathological point, the diagnosis of Parkinson's disease is confirmed by a neuronal cell loss and the presence of Lewy bodies in the substantia nigra. In Parkinson's disease, the precise type of nigral neuron which degenerate still remains unknown. Are all types of neuron similarly injured, are only subpopulations of neurons vulnerable? In an attempt to answer the question, a qualitative and quantitative analysis of the distribution of dopaminergic cells, as identified by immunohistochemistry with a specific antibody against tyrosine hydroxylase, was performed in the ventral mesencephalon of control subjects and patients who died with a clinical diagnosis of Parkinson's disease. In control brains, two types of catecholaminergic neurons were evidenced; some contain visible-neuromelanin, others do not. In patients with Parkinson's disease, the tyrosine hydroxylase positive cells which contained the pigment were the most vulnerable.

Dendritic arbors of spiny neurons in the primate striatum are directionally polarized.

Despite the relatively unfeatured cytoarchitecture of the striatum, this large subcortical region has been found to have a modular macroscopic substructure comprising the neurochemically distinct striosomes and matrix, and, within the matrix, patchy input and output arrangements called matrisomes. In the study reported here, we explored the possibility that the cellular architecture of the striatum is also more specialized than previously suspected. We injected medium spiny neurons in lightly fixed slices of the squirrel monkey caudate nucleus, reconstructed their dendritic arbors, and analyzed the orientations of these arbors with respect to the cardinal planes of the striatum. The data were unequivocal in suggesting that many spiny neurons, whether near striosomes or not, have dendritic arbors with preferred orientations along a diagonal axis running from rostral, dorsal, and medial to caudal, ventral, and lateral. This axis corresponds to the orientations of many striosomes and matrisomes in the squirrel monkey's caudate nucleus. We therefore suggest that the primate striatum is characterized not only by a macroscopic organization dividing it into striosomes and matrisomes, but also by a microscopic architecture observed by the dendritic arbors of many of its projection neurons. We obtained comparable supplementary observations for the ferret caudate nucleus, suggesting that such spatial alignment of spiny dendritic arbors may be a general feature of striatal organization. These polarized dendritic arrangements could provide a cellular framework for compartmental input-output processing within the striatum.

Species-specific patterns of glycoprotein expression in the developing rodent caudoputamen: association of 5'-nucleotidase activity with dopamine islands and striosomes in rat, but with extrastriosomal matrix in mouse.

The glycoprotein 5'-nucleotidase is a cell surface phosphatase and represents a new marker for striosomes in the adult rat caudoputamen. We report here on its developmental expression in the rat and mouse striatum, and show an unexpected converse 5'-nucleotidase chemoarchitecture of the caudoputamen in these closely related species. In the rat, 5'-nucleotidase activity was first visible as neuropil staining in tyrosine hydroxylase-positive dopamine islands of the midstriatum on postnatal day 1, and by the end of the first postnatal week, 5'-nucleotidase-positive dopamine islands also appeared rostrally. This compartmental pattern persisted thereafter, so that in adult animals, in all but the caudal caudoputamen, zones of enhanced 5'-nucleotidase staining were restricted to calbindin-D28k-poor striosomes. Weak 5'-nucleotidase activity also emerged in the matrix. In striking contrast, in the mouse striatum, enhanced 5'-nucleotidase activity was preferentially associated with extrastriosomal tissue. Enzymatic reaction first appeared on embryonic day 18, and developed over the first postnatal week into a mosaic pattern in which the matrix was stained but the dopamine islands were unstained. The matrix staining itself was heterogeneous. After the second postnatal week, most of the caudoputamen was stained, and in adult mice only rostral striosomes expressed low 5'-nucleotidase activity. We conclude that in rats, 5'-nucleotidase represents one of the few substances that maintains a preferential dopamine island/striosome distribution during striatal development. In mice, 5'-nucleotidase activity is expressed preferentially in the matrix during development, and its compartmental pattern is gradually lost with maturation, except very rostrally. These findings do not suggest an instructive role of the enzyme in striatal compartment formation in either species, but do suggest the possibility that 5'-nucleotidase contributes to the differentiation of striatal compartments during development.

Compartmental organization of the thalamostriatal connection in the cat.

The compartmental organization of the thalamostriatal connection in the cat was studied by labelling thalamic fibers in anterograde axonal transport experiments and comparing their striatal distributions with the arrangement of striosomes and matrix tissue identified by histochemical staining methods. When analyzed according to their principal compartmental targets in dorsal striatum, the thalamic deposits indicated the existence of medial and lateral divisions within the thalamostriatal projection. Nuclei of the medial division, which includes parts of the thalamic midline, projected primarily to striosomes. The lateral division, which embraces the anterior and posterior intralaminar groups, the rostral ventral tier nuclei, and parts of the posterior lateral nuclear complex, predominantly innervated matrix tissue. In the dorsal division of the nucleus accumbens, the medial system preferentially terminated in zones that stain heavily in butyrylcholinesterase and substance P preparations, but fibers from both the medial and the lateral systems largely avoided the histochemically marked compartments such as the border islands of the nucleus accumbens that are seen elsewhere in the ventral striatum. Medial division: Thalamic deposits involving the paraventricular and rhomboid nuclei of the thalamic midline elicited labelling of striosomes and, invariably, ventral extrastriosomal matrix, the nucleus accumbens, and the amygdala. This projection was topographically organized: rostral thalamic deposits elicited labelling in the medial caudate nucleus and the medial nucleus accumbens. More caudal injections produced more lateral labelling. Lateral division: The lateral division is composed of at least three projection systems distinguished by their patterns of matrix innervation. Deposits involving the anterior intralaminar nuclei and the striatally projecting cells located lateral to the stria medullaris (anterior intralaminar complex) produced an even, diffuse labelling of the matrix tissue and weak labelling of the striosomes. Injections placed in the ventroanterior, ventrolateral, and ventromedial nuclei (rostral ventral complex) elicited fibrous labelling of matrix tissue that often showed nonstriosomal inhomogeneities. Deposits involving the centromedian and parafascicular nuclei (posterior intralaminar complex) produced a highly variable pattern of matrix labelling that included both homogeneous and decidedly patchy innervations of the extrastriosomal matrix. Each of these lateral thalamostriatal systems showed a similar spatial organization, whereby dorsoventral and mediolateral thalamic axes were roughly preserved in the projection to striatum.

Ectosylvian visual area of the cat: location, retinotopic organization, and connections.

We have mapped out the ectosylvian visual area (EVA) of the cat in a series of single- and multiunit recording studies. EVA occupies 10-20 mm2 of cortex at the posterior end of the horizontal limb of the anterior ectosylvian sulcus. EVA borders on somatosensory cortex anteriorly, auditory cortex posteriorly, and nonresponsive cortex laterally. EVA exhibits limited retinotopic organization, as indicated by the fact that receptive fields shift gradually with tangential travel of the microelectrode through cortex. However, a point-to-point representation of the complete visual hemifield is not present. We have characterized the afferent and efferent connections of EVA by placing retrograde and anterograde tracer deposits in EVA and in other cortical visual areas. The strongest transcortical fiber projection to EVA arises in the lateral suprasylvian visual areas. Area 20, the granular insula, and perirhinal cortex provide additional sparse afferents. The projection from lateral suprasylvian cortex to EVA arises predominantly in layer 3 and terminates in layer 4. EVA projects reciprocally to all cortical areas from which it receives input. The projection from EVA to the lateral suprasylvian areas arises predominantly in layers 5 and 6 and terminates in layer 1. EVA is linked reciprocally to a thalamic zone encompassing the lateromedial-suprageniculate complex and the adjacent medial subdivision of the latero-posterior nucleus. We conclude that EVA is an exclusively visual area confined to the anterior ectosylvian sulcus and bounded by nonvisual cortex. EVA is distinguished from other visual areas by its physical isolation from those areas, by its lack of consistent global retinotopic organization, and by its placement at the end of a chain of areas through which information flows outward from the primary visual cortex.