Neuroimaging of Tactile Information Processing

Neural processing of tactile information in the brain has been relatively less unveiled compared to other senses, such as visual and auditory information. This is partly due to difficulties in creating tactile stimuli, a wide distribution of tactile receptors over the whole body, the lack of rich understanding of tactile perception, and tight coupling of tactile sensation with action. Nonetheless, it is important to understand how the central nervous system processes tactile information in order to develop clinical solutions for impairment of somatosensory systems, create artificial tactile systems for robots, and advance the assistive technology based on perception-action coupling for the elderly. In this review, we revisit recent investigations of neural processing of tactile information in the human brain using neuroimaging. In particular, this review focuses on cutaneous innocuous tactile information.

Modeling Long-term Spike Frequency Adaptation in SA-I Afferent Neurons Using an Izhikevich-based Biological Neuron Model

To develop a biomimetic artificial tactile sensing system capable of detecting sustained mechanical touch, we propose a novel biological neuron model (BNM) for slowly adapting type I (SA-I) afferent neurons. The proposed BNM is designed by modifying the Izhikevich model to incorporate long-term spike frequency adaptation. Adjusting the parameters renders the Izhikevich model describing various neuronal firing patterns. We also search for optimal parameter values for the proposed BNM to describe firing patterns of biological SA-I afferent neurons in response to sustained pressure longer than 1-second. We obtain the firing data of SA-I afferent neurons for six different mechanical pressure ranging from 0.1 mN to 300 mN from the ex-vivo experiment on SA-I afferent neurons in rodents. Upon finding the optimal parameters, we generate spike trains using the proposed BNM and compare the resulting spike trains to those of biological SA-I afferent neurons using the spike distance metrics. We verify that the proposed BNM can generate spike trains showing long-term adaptation, which is not achievable by other conventional models. Our new model may offer an essential function to artificial tactile sensing technology to perceive sustained mechanical touch.

Bias in Prestimulus Motor Cortical Activity Determines Decision-making Error in Rodents

Decision-making is a complex process that involves the integration and interpretation of sensory information to guide actions. The rodent motor cortex, which is generally involved in motor planning and execution, also plays a critical role in decision-making processes. In perceptual delayedresponse tasks, the rodent motor cortex can represent sensory cues, as well as the decision of where to move. However, it remains unclear whether erroneous decisions arise from incorrect encoding of sensory information or improper utilization of the collected sensory information in the motor cortex. In this study, we analyzed the rodent anterior lateral motor cortex (ALM) while the mice performed perceptual delayed-response tasks. We divided population activities into sensory and choice signals to separately examine the encoding and utilization of sensory information.We found that the encoding of sensory information in the error trials was similar to that in the hit trials, whereas choice signals evolved differently between the error and hit trials. In error trials, choice signals displayed an offset in the opposite direction of instructed licking even before stimulus presentation, and this tendency gradually increased after stimulus onset, leading to incorrect licking. These findings suggest that decision errors are caused by biases in choice-related activities rather than by incorrect sensory encoding. Our study elaborates on the understanding of decisionmaking processes by providing neural substrates for erroneous decisions.

Differential Encoding of Trace and Delay Fear Memory in the Entorhinal Cortex

Trace fear conditioning is characterized by a stimulus-free trace interval (TI) between the conditioned stimulus (CS) and the unconditioned stimulus (US), which requires an array of brain structures to support the formation and storage of associative memory. The entorhinal cortex (EC) has been proposed to provide essential neural code for resolving temporal discontinuity in conjunction with the hippocampus. However, how the CS and TI are encoded at the neuronal level in the EC is not clear. In Exp. 1, we tested the effect of bilateral pre-training electrolytic lesions of EC on trace vs. delay fear conditioning using rats as subjects. We found that the lesions impaired the acquisition of trace but not delay fear conditioning confirming that EC is a critical brain area for trace fear memory formation. In Exp. 2, single-unit activities from EC were recorded during the pretraining baseline and post-training retention sessions following trace or delay conditioning. The recording results showed that a significant proportion of the EC neurons modulated their firing during TI after the trace conditioning, but not after the delay fear conditioning. Further analysis revealed that the majority of modulated units decreased the firing rate during the TI or the CS. Taken together, these results suggest that EC critically contributes to trace fear conditioning by modulating neuronal activity during the TI to facilitate the association between the CS and US across a temporal gap.

Implantable Neural Probes for Brain-Machine Interfaces – Current Developments and Future Prospects

A Brain-Machine interface (BMI) allows for direct communication between the brain and machines. Neural probes for recording neural signals are among the essential components of a BMI system. In this report, we review research regarding implantable neural probes and their applications to BMIs. We first discuss conventional neural probes such as the tetrode, Utah array, Michigan probe, and electroencephalography (ECoG), following which we cover advancements in next-generation neural probes. These next-generation probes are associated with improvements in electrical properties, mechanical durability, biocompatibility, and offer a high degree of freedom in practical settings. Specifically, we focus on three key topics: (1) novel implantable neural probes that decrease the level of invasiveness without sacrificing performance, (2) multi-modal neural probes that measure both electrical and optical signals, (3) and neural probes developed using advanced materials. Because safety and precision are critical for practical applications of BMI systems, future studies should aim to enhance these properties when developing next-generation neural probes.

An Angiography Study of the Colon Artery from the Superior Mesenteric Artery

Incorporation of laparoscopic techniques into the gastrointestinal surgeon's armamentarium has led to a renewal of interest in the anatomy of mesenteric arteries because hemorrhagic complications can be a major cause of conversion and/or morbidity during laparoscopic intestinal surgery. BACKGROUND: Since a colonic resection with laparoscopic techniques has become a common procedure, the limited exposure currently provided in laparoscopic intestinal resection demands a precise knowledge of mesenteric vascular anatomy to avoid such complications and to expedite the procedure. Historically, It was thought that the arterial supply to the right colon consisted of three arterial branches (middle colic artery, right colic artery, ileocolic artery) arising independently from the superior mesenteric artery (SMA). However, on recent reports and clinical observations, two colonic arteries only arising independently from the SMA are more common than three colonic arteries. METHODS: We reviewed 40 cases of angiography which focused on the SMA and it's branches. RESULTS: We found the ileocolic artery in 39 of 40 cases, the middle colic artery in 39 of 40, and the right colic artery in 19 of 40. Based on the existence of the right colic artery in our review, about half (47.5%) of the cases had a right colic artery directly arising from this SMA. CONCLUSION: This knowledge may help lower the risk of vascular complications during laparoscopic intestinal surgery.