Implicit Memory in Monkeys: Development of a Delay Eyeblink Conditioning System with Parallel Electromyographic and High-Speed Video Measurements

Abstract

Delay eyeblink conditioning, a cerebellum-dependent learning paradigm, has been applied to various mammalian species but not yet to monkeys. We therefore developed an accurate measuring system that we believe is the first system suitable for delay eyeblink conditioning in a monkey species (Macaca mulatta). Monkey eyeblinking was simultaneously monitored by orbicularis oculi electromyographic (OO-EMG) measurements and a high-speed camera-based tracking system built around a 1-kHz CMOS image sensor. A 1-kHz tone was the conditioned stimulus (CS), while an air puff (0.02 MPa) was the unconditioned stimulus. EMG analysis showed that the monkeys exhibited a conditioned response (CR) incidence of more than 60% of trials during the 5-day acquisition phase and an extinguished CR during the 2-day extinction phase. The camera system yielded similar results. Hence, we conclude that both methods are effective in evaluating monkey eyeblink conditioning. This system incorporating two different measuring principles enabled us to elucidate the relationship between the actual presence of eyelid closure and OO-EMG activity. An interesting finding permitted by the new system was that the monkeys frequently exhibited obvious CRs even when they produced visible facial signs of drowsiness or microsleep. Indeed, the probability of observing a CR in a given trial was not influenced by whether the monkeys closed their eyelids just before CS onset, suggesting that this memory could be expressed independently of wakefulness. This work presents a novel system for cognitive assessment in monkeys that will be useful for elucidating the neural mechanisms of implicit learning in nonhuman primates.

Development of a low-cost, user-customizable, high-speed camera

“…Research has also investigated the relationship between trans-glottal airflow and vocal fold vibration (recorded at 1900 fps at 256x64 resolution) [48], with more recent work analyzing the effect of resolution on the laryngeal parameters computed on the captured glottal area waveform (4000 fps, resolutions at or below 512x256) [49]. Even a study in delay eyeblink conditioning in monkeys [50] had required high-speed video measurements at 2421 fps and 128x128 pixels, a configuration similar to what our camera can achieve. Moreover, popular technology reviewers use high-speed imaging to perform comparisons or verify commercial product claims.…”

The Use of Trace Eyeblink Classical Conditioning to Assess Hippocampal Dysfunction in a Rat Model of Fetal Alcohol Spectrum Disorders

“…ECC is a paradigm that has been utilized for more than a century to scientifically investigate the fundamental basis of learning 26 27 and as such, provides a useful method to better understanding the adverse neurocognitive consequences resulting from fetal alcohol exposure. It is a very flexible paradigm that allows investigators to use a variety of different ECC procedures, any of which can be examined across many mammalian species ascending the phylogenetic scale (from mice to humans) and over different courses of brain development 28 29 30 31 . Furthermore, the fundamental neural circuits that mediate associative learning in this paradigm are supported by experimental and neuropsychological reports in these same species 26 32 33 34 35 36 37 .…”