Artificial Photothermal Nociceptor Using Mott Oscillators

Abstract

Bioinspired sensory systems based on spike neural networks have received considerable attention in resolving high energy consumption and limited bandwidth in current sensory systems. To efficiently produce spike signals upon exposure to external stimuli, compact neuron devices are required for signal detection and their encoding into spikes in a single device. Herein, it is demonstrated that Mott oscillative spike neurons can integrate sensing and ceaseless spike generation in a compact form, which emulates the process of evoking photothermal sensing in the features of biological photothermal nociceptors. Interestingly, frequency-tunable and repetitive spikes are generated above the threshold value (P_th = 84 mW cm^-2) as a characteristic of "threshold" in leaky-integrate-and-fire (LIF) neurons; the neuron devices successfully mimic a crucial feature of biological thermal nociceptors, including modulation of frequency coding and startup latency depending on the intensity of photothermal stimuli. Furthermore, Mott spike neurons are self-adapted after sensitization upon exposure to high-intensity electromagnetic radiation, which can replicate allodynia and hyperalgesia in a biological sensory system. Thus, this study presents a unique approach to capturing and encoding environmental source data into spikes, enabling efficient sensing of environmental sources for the application of adaptive sensory systems.

Keywords: artificial nociceptor; metal‐insulator transition; neuron; oscillator; oxide.

Figure 1

Demonstration of bio‐inspired artificial nerves using Mott oscillators. a) Illustration of a biological nociceptor: When a stimulus is received from a nerve ending, the nociceptive neuron compares the signal's amplitude with a threshold value, deciding whether to generate an action potential and send it to the cortex via the spinal cord. b) the artificial nociceptor for detecting electromagnetic radiation: Upon illumination, the artificial nociceptor detects light and generates a spike only when the light intensity is high enough to trigger the oscillator. c) Plane‐view scanning electron microscopy (SEM) image of VO₂ threshold switch connected in series with a resistor. d) Oscillative spike neurons based on Pearson‐Anson circuits consisting of a VO₂ threshold switch, a parasitic capacitor, and a series resistor.

Figure 2

Artificial photothermal nociceptors using Mott oscillators. a) Current‐triggered threshold switching in VO₂ in dark conditions (black line) and under exposure to infrared light radiation (red line, P = 280 mW cm⁻²). The exposure to infrared light radiation resulted in a decrease in the threshold current (I_th  = 447 µA→413 µA) and the reduction of corresponding threshold V_{out, th} (=9.04 V→6.81 V) across VO₂ thin films. b) Description of the artificial nociceptor circuit for light‐triggered spike oscillation of V_out . c) Frequency‐tunable and repetitive V_out spike generation upon infrared radiation exposure with different P. d) Enlarged view of spike‐encoded output at the maximum frequency (f_max ) from c. e) Encoded frequency as a function of time after the initiation of spike generation. The frequency gradually increased and saturated at the maximum frequency (f_max ). The parameters of the spikes generated (t_inc , f_max ) in our artificial nerve systems with the increase of temperature f) and infrared radiation g). The similarity of parameters strongly supports photothermal absorption on VO₂ films as the origin of photo‐triggered spike generation.

Figure 3

History‐dependent sensitization of our artificial nociceptor under intense photo‐stimulation. a) The spike frequency response of artificial nociceptors under three consecutive infrared pulses (P₁ , P₂ , and P ₃, with P ₂ > P ₁ = P ₃). High intensity of infrared radiation (i.e., P₂ = 280 mW cm⁻²) sensitized the artificial VO₂ nociceptor; this sensitized nociceptor, after exposure to high radiation, strongly changes t_inc and f_max . b) Enlarged view of spike‐encoded output in normal and sensitized states before and after the exposure of P₂ , respectively. c) The spike frequency response of the VO₂ artificial nociceptor in a sensitized state with different P ₁ and P ₃. d) More exaggerated responses in a sensitized state in the VO₂ artificial nociceptor, which mimics allodynia and hyperalgesia in a biological nociceptor. e) Sensitization characteristics of our nociceptor (i.e., allodynia and hyperalgesia), especially these key features, align with those of the biological nociceptor.

Figure 4

Demonstration of broadband light‐responsive artificial nociceptor. Frequency‐tunable and repetitive V_out spike generation upon UV a) and visible light f) radiation exposure with different P. Encoded frequency as a function of time after the initiation of spike generation: UV b), visible light g). The parameters of the spikes generated (t_inc , f_max ) in our artificial nerve systems with the increase of light intensity: UV c), visible light h). Spike‐encoded output in normal and sensitized states before and after the exposure of P₂ : UV d), visible light i). More exaggerated responses in a sensitized state in the VO₂ artificial nociceptor, which mimic allodynia and hyperalgesia in a biological nociceptor: UV e), visible light j).