Reward representations and reward-related learning in the human brain: insights from neuroimaging

This review outlines recent findings from human neuroimaging concerning the role of a highly interconnected network of brain areas including orbital and medial prefrontal cortex, amygdala, striatum and dopaminergic mid-brain in reward processing. Distinct reward-related functions can be attributed to different components of this network. Orbitofrontal cortex is involved in coding stimulus reward value and in concert with the amygdala and ventral striatum is implicated in representing predicted future reward. Such representations can be used to guide action selection for reward, a process that depends, at least in part, on orbital and medial prefrontal cortex as well as dorsal striatum.     

Unconventional sex: fresh approaches to courtship learning

Understanding the complex array of genes, proteins and cells involved in learning and memory is a major challenge for neuroscientists. Using the genetically powerful model system, Drosophila melanogaster, and its well-studied courtship behavior, investigators have begun to delineate essential elements of associative and nonassociative behavioral plasticity. Advances in transgenic tools and developments in behavioral assays have increased the power of studying courtship learning in the fruit fly.     

New concepts of the supplementary motor area

The supplementary motor area, although traditionally defined as a single motor area, is not viewed as including at least three different areas that can be distinguished anatomically and physiologically. The differential use of these three areas for various motor behaviors has been the subject of recent studies that are beginning to provide novel concepts of the functional differentiation of each area.     

Interactions between motor commands and somatic perception in sensorimotor cortex

For many years, it has been postulated that interactions between motor commands and somatic perception in the sensorimotor cortices exist, but they have been difficult to demonstrate. Recent studies have made demonstration of this interaction easier and suggest that cortical activity related to somatic sensation and perception is modified by movement-generating mechanism. Corollary discharge and efference copy may also play a role in motor behavior.     

The mechanism and control of cytokinesis

Cytokinesis is under active investigation in each of the dominant experimental model systems. During 1996 and 1997, several developments necessitated the reassessment of the prevailing model for cytokinesis. In addition, the inventory of proteins required for cytokinesis has grown considerably. However, a molecular understanding of cytokinesis still remains elusive.     

Biorobotic approaches to the study of motor systems

Biorobotics is a promising new area of research at the interface between biology and robotics. Robots can either be used as physical models of biological systems or be directly inspired by biological studies. A great deal of progress has recently been made in biorobotic studies of locomotion, orientation, and vertebrate arm control.     

A role for the cerebellum in the control of limb movement velocity

Accepting, rejecting or modifying the many different theories of the cerebellum's role in the control of movement requires an understanding of the signals encoded in the discharge of cerebellar neurons and how those signals are transformed by the cerebellar circuitry. Particularly challenging is understanding the sensory and motor signals carried by the two types of action potentials generated by cerebellar Purkinje cells, the simple spikes and complex spikes. Advances have been made in understanding this signal processing in the context of voluntary arm movements. Recent evidence suggests that mossy fiber afferents to the cerebellar cortex are a source of kinematic signals, providing information about movement direction and speed. In turn, the simple spike discharge of Purkinje cells integrates this mossy fiber information to generate a movement velocity signal. Complex spikes may signal errors in movement velocity. It is proposed that the cerebellum uses the signals carried by the simple and complex spike discharges to control movement velocity for both step and tracking arm movements.     

On growth and form: control of cell morphogenesis in fission yeast

In the past year, we have gained considerable insight into the process of cell morphogenesis and the establishment of positional information in fission yeast. The highlights include a better understanding of the role of the microtubule cytoskeleton in the control of cell shape, as well as the identification of novel genes essential for the establishment of cell polarity and for the positioning of the site of cell division.     

The integration of microarray information in the drug development process

In the past year, microarray technologies have moved beyond the proof-of-principle stage. Microarrays are now being used for genome-wide expression monitoring, large-scale polymorphism screening and mapping, and for the evaluation of drug candidates.     

The chemical-biological interface: developments in automated and miniaturised screening technology

The rapidly changing developments in genomics and combinatorial chemistry, generating new drug targets and large numbers of compounds, have caused a revolution in high-throughput screening technologies. Key to this revolution has been the introduction of robotics and automation, together with new biological assay technologies (e.g., homogeneous time resolved fluorescence). With ever increasing workloads, together with economic and logistical constraints, miniaturisation is rapidly becoming essential for the future of high-throughput screening and combinatorial chemistry. This is evident from the introduction of high-density microtitre plates, small volume liquid handling robots and associated detection technology.     

The restriction point and control of cell proliferation

Research over the past two decades has defined a window of time in the early/mid G₁ phase of the cell cycle during which mammalian cells are responsive to extracellular signals. Recent evidence indicates that this period ends with the phosphorylation of the retinoblastoma protein, enabling the cells to pass through the restriction point at the end of mid G₁ phase and to commit to completing the remaining phases of the growth cycle.     

Coordinate control of secondary metabolite production and asexual sporulation in Aspergillus nidulans

Microbial secondary metabolite production is frequently associated with developmental processes such as sporulation, but there are few cases where this correlation is understood. Recent work with the filamentous fungus Aspergillus nidulans has provided new insights into the mechanisms coordinating production of the toxic secondary metabolite sterigmatocystin with asexual sporulation. These processes have been shown to be linked through a common need to inactivate a heterotrimeric G protein dependent signaling pathway that, when active, serves to stimulate growth while blocking both sporulation and sterigmatocystin biosynthesis.     

Cortical control of reaching movements

Recent studies provide further support for the hypothesis that spatial representations of limb position, target locations, and potential motor actions are expressed in the neuronal activity in parietal cortex. In contrast, precentral cortical activity more strongly expresses processes involved in the selection and execution of motor actions. As a general conceptual framework, these processes may be interpreted in terms of such formalisms as sensorimotor transformation and ‘internal models’.     

Ionic currents, transmitters and models of motor pattern generators

Recent work, combining direct study of ion channels and synapses with pharmacological manipulations and realistic computer simulations, has deepened our understanding of how motor circuits produce rhythmic outputs. In several preparations, both the roles of some key ionic currents in circuit operation and the mechanisms by which circuit operation may be modulated have been identified.     

Dimorphism and virulence in Candida albicans

Two regulatory pathways govern filamentation in the pathogenic fungus Candida albicans. Recent virulence studies of filamentation regulatory mutants argue that both yeast and filamentous forms have roles in infection. Filamentation control pathways seem closely related in C. albicans and in Saccharomyces cerevisiae, thus permitting speculation about C. albicans filamentation genes not yet discovered.     

Inertial vestibular coding of motion: concepts and evidence

Central processing of inertial sensory information about head attitude and motion in space is crucial for motor control. Vestibular signals are coded relative to a non-inertial system, the head, that is virtually continuously in motion. Evidence for transformation of vestibular signals from head-fixed sensory coordinates to gravity-centered coordinates have been provided by studies of the vestibulo-ocular reflex. The underlying central processing depends on otolith afferent information that needs to be resolved in terms of head translation related inertial forces and head attitude dependent pull of gravity. Theoretical solutions have been suggested, but experimental evidence is still scarce. It appears, along these lines, that gaze control systems are intimately linked to motor control of head attitude and posture.