Suguru N. Kudoh

Fundamental short-term memory of semi-artificial neuronal network

Spatiotemporal pattern of neuronal network activity is a key component of brain information processing. Cultured rat hippocampal neurons on the multielectrodes array dish are suitable for analyzing and manipulating network dynamics and its developmental changes. We applied paired electrical inputs at various inter-stimulus intervals (ISi) and analyzed the spatio-temporal pattern of evoked responses. We found that the pattern of evoked electrical activity was affected by existence of a prior input in the case that ISi of paired stimuli was within 2 s. These results suggest that a semi-artificial neuronal network on a culture dish has a fundamental component of short-term memory, and the origin of this hysteresis is transition among the internal states of the network, undertaken by synaptic transmissions.

Neurorobot Vitroid — A living test model for embodiment brain research

One of effective approaches to problems of conventional artificial intelligence is embodied cognitive science. To realize an embodiment of a cultured living neuronal circuit, we provided cultured neurons with a body of a miniature-moving robot. The aim of this neuro-robot system is preparing a testing environment of the suitable relationship between activity of living neuronal network (LNN) and phenomena in outside world. We call our neuro-robot system as ”Vitroid, meaning a system as a kind of a “test tube” for cognitive agent made by living component. We have investigated whether the Vitroid with various algorithms for linking neurons and outer world can be embedded a certain a priori behavior, and elucidated the modification of network dynamics induced by robot behaviors. We have developed Vitroid with simplified fuzzy reasoning, and a weighted averaging of selected electrode activity. Both algorithms for linking induced the decrease of standard deviation of the number of electrical events induced by inputs from sensor on the robot. It suggests that the modification of network dynamics is induced by robot behaviors, which is likely in animal brain.

Does Representation of Outer Objects in Living Neuronal Network Synthesize “the concept”?

Cultured living neuronal network with input-output-interface is the useful model to investigate how to autonomously create an internal object. Using living neuronal network cultured on a multielectrodes-array-dish, We elucidated the relationships between activity patterns evoked by inputs to 3 different electrodes. Activity patterns evoked by 3 different inputs were classified into several clusters including patterns evoked by 3 inputs at various ratios. Repeated input in stable temporal pattern led the clusters to fuse into single cluster. These results indicated that the Cultured living neuronal network (CLNN) separates and classifies the input from outer world and distinguished clusters are autonomously formed.

Surface plasmon-enhanced optical trapping of quantum-dot-conjugated surface molecules on neurons cultured on a plasmonic chip

Living neurons in a complex neuronal network communicate with each other through synaptic connections. The molecular dynamics of cell surface molecules localized at synaptic terminals is essential for functional connections via synaptic plasticity in the neuronal network. Here, we demonstrate surface-plasmon-resonance-based optical trapping using a plasmonic chip toward realizing effective manipulation of molecules on the surface of neurons. Surface-plasmon-enhanced optical trapping was evaluated by the fluorescence analysis of nanoparticles suspended in water and neural cell adhesion molecules (NCAMs) labeled with quantum dots (Q-dots) on rat hippocampal neurons. The motion of nanoparticles in water and the molecular dynamics of NCAMs on neuronal cells cultured on a plasmonic chip were constrained at the laser focus more effectively than those on a glass substrate because of the surface plasmon resonance effect.

Relationship between inter-stimulus-intervals and intervals of autonomous activities in a neuronal network

To investigate relationships between neuronal network activity and electrical stimulus, we analyzed autonomous activity before and after electrical stimulus. Recordings of autonomous activity were performed using dissociated culture of rat hippocampal neurons on a multi-electrodes array (MEA) dish. Single stimulus and pared stimuli were applied to a cultured neuronal network. Single stimulus was applied every 1 min, and paired stimuli was performed by two sequential stimuli every 1 min. As a result, the patterns of synchronized activities of a neuronal network were changed after stimulus. Especially, long range synchronous activities were induced by paired stimuli. When 1 s inter-stimulus-intervals (ISI) and 1.5 s ISI paired stimuli are applied to a neuronal network, relatively long range synchronous activities expressed in case of 1.5 s ISI. Temporal synchronous activity of neuronal network is changed according to inter-stimulus-intervals (ISI) of electrical stimulus. In other words, dissociated neuronal network can maintain given information in temporal pattern and a certain type of an information maintenance mechanism was considered to be implemented in a semi-artificial dissociated neuronal network. The result is useful toward manipulation technology of neuronal activity in a brain system.

The effects of transient abolishment of electrical activity on dynamics in a dissociated neuronal network

The higher-order functions of brain depend on neuronal network electrical activity with complex spatiotemporal patterns. The background activity, such as spontaneous electrical activity observed in a dissociated culture of rat hippocampal neurons, is considered to be a fundamental component of internal state of the living neuronal network. The spontaneous activity has dynamic and complicated spatiotemporal activity patterns, thus it is uncertain that transiently discontinued activity pattern recovers to the same activity state. We elucidated the stability of the internal state of network activity after a transient abolishment of neuronal electrical activity. As a result, spontaneous activity pattern became to be bursting and intermittent pattern after the transient block of electrical activity. In addition, spontaneous neuronal activity increased in frequency. These modified patterns lasted for hours then gradually returned to the initial state. These results suggest that steady state of spontaneous activity is a result of complex equilibrium of interactions between neurons. Thus, it is required to consider the influence of the inhibition itself when the neural activity is stopped by pharmacological manipulations.

Stability of neuronal electrical activity pattern evoked by two inputs stimulation

Rat hippocampal dissociated culture on multi electrodes array dish (MED) is useful as minimalized brain model to investigation of principles of brain information processing. Rat hippocampal neuronal cells were cultured on MED with 64 microelectrodes and they reconstructed a complex network. We analyzed stability of neuronal electrical activity pattern after two distinct electrical stimuli. Distances between averaged spike pattern and spike pattern after electrical stimulation for summarizing the activity pattern to temporal axis direction and trial (sweep) axis direction. The distances of the analysis for summarized to temporal axis direction increased immediately after stimulation and after it, recovered to standard level. Moreover, stabilizing points emerge every 100 ms on both analysis for summarizing the activity pattern to temporal axis direction and trial axis direction. These results suggest that the neural network buttress by electrical stimulation and it be complex by two-point inputs.

Validation of long-term changes of evoked response with self-orgnization map

In order to analyze stability of stimulation evoked neuronal activity, it is necessary to analyze long-term changes of evoked response pattern induced by electrical stimulation. For this purpose, we use Self-Organization-Map (SOM), which continuously performs non-teacher learning. Neural network was alternately stimulated by two different electrodes. SOM maps to response pattern induced by each electrical stimulation in 30 × 30-2D space. Only at the first stage of the learning, SOM is forced to select a specific winner nodes previously assigned in order to associate a specific node to the input vector. We call the process seeding. After seeding procedure, the winner units correspond to the response patterns induced by two different inputs are separately mapped. We confirmed that response patterns of electrical stimulation were stimulation specific and they were almost stable. In addition, Not small part of spontaneous activities share the activity patterns with evoked responses, suggesting that inputs were not tightly coupled to their response patterns.

Functional connections between avian and mammalian neurons

The genetical controls are critical for constructing specific circuit in a brain, however, also a distant relationship likes a mammal and a bird, the fundamental structure and functions of neurons are preserved. Using Ca2+ imaging of a mixed culture of rat and chick neurons, we elucidated whether the functional connections are formed between neurons from relatively distant species in this study. Periodic and synchronized Ca2+ transients were often observed. Some synchronizations were not strict, suggesting that the bursting activity was loosely transmitted each other. A coculture of rat and chick neuronal cells was possible and some of neurons from distinct species made functional connections, which can be utilized to complementation of damaged neuronal circuit. The mixed circuit of cultured neurons from distinct species is the interesting testing platform for elucidating conditions required for a synaptogenesis and activity of a circuit of neurons from mixed species.