The role of the optic tectum for visually evoked orienting and evasive movements.

As animals forage for food and water or evade predators, they must rapidly decide what visual features in the environment deserve attention. In vertebrates, this visuomotor computation is implemented within the neural circuits of the optic tectum (superior colliculus in mammals). However, the mechanisms by which tectum decides whether to approach or evade remain unclear, and also which neural mechanisms underlie this behavioral choice. To address this problem, we used an eye-brain-spinal cord preparation to evaluate how the lamprey responds to visual inputs with distinct stimulus-dependent motor patterns. Using ventral root activity as a behavioral readout, we classified 2 main types of fictive motor responses: (i) a unilateral burst response corresponding to orientation of the head toward slowly expanding or moving stimuli, particularly within the anterior visual field, and (ii) a unilateral or bilateral burst response triggering fictive avoidance in response to rapidly expanding looming stimuli or moving bars. A selective pharmacological blockade revealed that the brainstem-projecting neurons in the deep layer of the tectum in interaction with local inhibitory interneurons are responsible for selecting between these 2 visually triggered motor actions conveyed through downstream reticulospinal circuits. We suggest that these visual decision-making circuits had evolved in the common ancestor of vertebrates and have been conserved throughout vertebrate phylogeny.

Direct Dopaminergic Projections from the SNc Modulate Visuomotor Transformation in the Lamprey Tectum.

Dopamine neurons in the SNc play a pivotal role in modulating motor behavior via striatum. Here, we show that the same dopamine neuron that targets striatum also sends a direct branch to the optic tectum (superior colliculus). Whenever SNc neurons are activated, both targets will therefore be affected. Visual stimuli (looming or bars) activate the dopamine neurons coding saliency and also elicit distinct motor responses mediated via tectum (eye, orienting or evasive), which are modulated by the dopamine input. Whole-cell recordings from tectal projection neurons and interneurons show that dopamine, released by SNc stimulation, increases or decreases the excitability depending on whether they express the dopamine D1 or the D2 receptor. SNc thus exerts its effects on the visuomotor system through a combined effect directly on tectum and also via striatum. This direct SNc modulation will occur regardless of striatum and represents a novel mode of motor control.

Spatiotemporal interplay between multisensory excitation and recruited inhibition in the lamprey optic tectum.

Animals integrate the different senses to facilitate event-detection for navigation in their environment. In vertebrates, the optic tectum (superior colliculus) commands gaze shifts by synaptic integration of different sensory modalities. Recent works suggest that tectum can elaborate gaze reorientation commands on its own, rather than merely acting as a relay from upstream/forebrain circuits to downstream premotor centers. We show that tectal circuits can perform multisensory computations independently and, hence, configure final motor commands. Single tectal neurons receive converging visual and electrosensory inputs, as investigated in the lamprey - a phylogenetically conserved vertebrate. When these two sensory inputs overlap in space and time, response enhancement of output neurons occurs locally in the tectum, whereas surrounding areas and temporally misaligned inputs are inhibited. Retinal and electrosensory afferents elicit local monosynaptic excitation, quickly followed by inhibition via recruitment of GABAergic interneurons. Multisensory inputs can thus regulate event-detection within tectum through local inhibition without forebrain control.

Tectal microcircuit generating visual selection commands on gaze-controlling neurons.

The optic tectum (called superior colliculus in mammals) is critical for eye-head gaze shifts as we navigate in the terrain and need to adapt our movements to the visual scene. The neuronal mechanisms underlying the tectal contribution to stimulus selection and gaze reorientation remains, however, unclear at the microcircuit level. To analyze this complex--yet phylogenetically conserved--sensorimotor system, we developed a novel in vitro preparation in the lamprey that maintains the eye and midbrain intact and allows for whole-cell recordings from prelabeled tectal gaze-controlling cells in the deep layer, while visual stimuli are delivered. We found that receptive field activation of these cells provide monosynaptic retinal excitation followed by local GABAergic inhibition (feedforward). The entire remaining retina, on the other hand, elicits only inhibition (surround inhibition). If two stimuli are delivered simultaneously, one inside and one outside the receptive field, the former excitatory response is suppressed. When local inhibition is pharmacologically blocked, the suppression induced by competing stimuli is canceled. We suggest that this rivalry between visual areas across the tectal map is triggered through long-range inhibitory tectal connections. Selection commands conveyed via gaze-controlling neurons in the optic tectum are, thus, formed through synaptic integration of local retinotopic excitation and global tectal inhibition. We anticipate that this mechanism not only exists in lamprey but is also conserved throughout vertebrate evolution.

The lamprey pallium provides a blueprint of the mammalian motor projections from cortex.

BACKGROUND: The frontal lobe control of movement in mammals has been thought to be a specific function primarily related to the layered neocortex with its efferent connections. In contrast, we now show that the same basic organization is present even in one of the phylogenetically oldest vertebrates, the lamprey. RESULTS: Stimulation of specific sites in the pallium/cortex evokes eye, trunk, locomotor, or oral movements. The pallial projection neurons target brainstem motor centers and basal ganglia subnuclei and have prominent dendrites extending into the outer molecular layer. They exhibit the characteristic features of pyramidal neurons and elicit monosynaptic glutamatergic excitatory postsynaptic potentials in output neurons of the optic tectum, reticulospinal neurons, and, as shown earlier, basal ganglia neurons. CONCLUSIONS: Our results demonstrate marked similarities in the efferent functional connectivity and control of motor behavior between the lamprey pallium and mammalian neocortex. Thus, the lamprey motor pallium/cortex represents an evolutionary blueprint of the corresponding mammalian system.

Gating of steering signals through phasic modulation of reticulospinal neurons during locomotion.

The neural control of movements in vertebrates is based on a set of modules, like the central pattern generator networks (CPGs) in the spinal cord coordinating locomotion. Sensory feedback is not required for the CPGs to generate the appropriate motor pattern and neither a detailed control from higher brain centers. Reticulospinal neurons in the brainstem activate the locomotor network, and the same neurons also convey signals from higher brain regions, such as turning/steering commands from the optic tectum (superior colliculus). A tonic increase in the background excitatory drive of the reticulospinal neurons would be sufficient to produce coordinated locomotor activity. However, in both vertebrates and invertebrates, descending systems are in addition phasically modulated because of feedback from the ongoing CPG activity. We use the lamprey as a model for investigating the role of this phasic modulation of the reticulospinal activity, because the brainstem-spinal cord networks are known down to the cellular level in this phylogenetically oldest extant vertebrate. We describe how the phasic modulation of reticulospinal activity from the spinal CPG ensures reliable steering/turning commands without the need for a very precise timing of on- or offset, by using a biophysically detailed large-scale (19,600 model neurons and 646,800 synapses) computational model of the lamprey brainstem-spinal cord network. To verify that the simulated neural network can control body movements, including turning, the spinal activity is fed to a mechanical model of lamprey swimming. The simulations also predict that, in contrast to reticulospinal neurons, tectal steering/turning command neurons should have minimal frequency adaptive properties, which has been confirmed experimentally.

Independent circuits in the basal ganglia for the evaluation and selection of actions.

The basal ganglia are critical for selecting actions and evaluating their outcome. Although the circuitry for selection is well understood, how these nuclei evaluate the outcome of actions is unknown. Here, we show in lamprey that a separate evaluation circuit, which regulates the habenula-projecting globus pallidus (GPh) neurons, exists within the basal ganglia. The GPh neurons are glutamatergic and can drive the activity of the lateral habenula, which, in turn, provides an indirect inhibitory influence on midbrain dopamine neurons. We show that GPh neurons receive inhibitory input from the striosomal compartment of the striatum. The striosomal input can reduce the excitatory drive to the lateral habenula and, consequently, decrease the inhibition onto the dopaminergic system. Dopaminergic neurons, in turn, provide feedback that inhibits the GPh. In addition, GPh neurons receive direct projections from the pallium (cortex in mammals), which can increase the GPh activity to drive the lateral habenula to increase the inhibition of the neuromodulatory systems. This circuitry, thus, differs markedly from the "direct" and "indirect" pathways that regulate the pallidal (e.g., globus pallidus) output nuclei involved in the control of motion. Our results show that a distinct reward-evaluation circuit exists within the basal ganglia, in parallel to the direct and indirect pathways, which select actions. Our results suggest that these circuits are part of the fundamental blueprint that all vertebrates use to select actions and evaluate their outcome.

Optimal control of gaze shifts.

To explore the visible world, human beings and other primates often rely on gaze shifts. These are coordinated movements of the eyes and head characterized by stereotypical metrics and kinematics. It is possible to determine the rules that the effectors must obey to execute them rapidly and accurately and the neural commands needed to implement these rules with the help of optimal control theory. In this study, we demonstrate that head-fixed saccades and head-free gaze shifts obey a simple physical principle, "the minimum effort rule." By direct comparison with existing models of the neural control of gaze shifts, we conclude that the neural circuitry that implements the minimum effort rule is one that uses inhibitory cross talk between independent eye and head controllers.

Identifying constituents in commercial gasoline using Fourier transform-infrared spectroscopy and independent component analysis.

A new method is proposed that enables the identification of five refinery fractions present in commercial gasoline mixtures using infrared spectroscopic analysis. The data analysis and interpretation was carried out based on independent component analysis (ICA) and spectral similarity techniques. The FT-IR spectra of the gasoline constituents were determined using the ICA method, exclusively based on the spectra of their mixtures as a blind separation procedure, i.e. assuming unknown the spectra of the constituents. The identity of the constituents was subsequently determined using similarity measures commonly employed in spectra library searches against the spectra of the constituent components. The high correlation scores that were obtained in the identification of the constituents indicates that the developed method can be employed as a rapid and effective tool in quality control, fingerprinting or forensic applications, where gasoline constituents are suspected.