Shared and unique features of mammalian sleep spindles – insights from new and old animal models

Abstract

Sleep spindles are phasic events observed in mammalian non-rapid eye movement sleep. They are relevant today in the study of memory consolidation, sleep quality, mental health and ageing. We argue that our advanced understanding of their mechanisms has not exhausted the utility and need for animal model work. This is both because some topics, like cognitive ageing, have not yet been addressed sufficiently in comparative efforts and because the evolutionary history of this oscillation is still poorly understood. Comparisons across species often are either limited to referencing the classical cat and rodent models, or are over-inclusive, uncritically including reports of sleep spindles in rarely studied animals. In this review, we discuss the emergence of new (dog and sheep) models for sleep spindles and compare the strengths and shortcomings of new and old models based on the three validation criteria for animal modelsface, predictive, and construct validity. We conclude that an emphasis on cognitive ageing might dictate the future of comparative sleep spindle studies, a development that is already becoming visible in studies on dogs. Moreover, reconstructing the evolutionary history of sleep spindles will require more stringent criteria for their identification, across more species. In particular, a stronger emphasis on construct and predictive validity can help verify if spindle-like events in other species are actual sleep spindles. Work in accordance with such stricter validation suggests that sleep spindles display more universally shared features, like defining frequency, than previously thought.

Alterations of sensory cell activity in the thalamic reticular nucleus by prefrontal cortex activation in anesthetized rats

“…In the second animal, the frequency band showing the largest power in A2 was the delta frequency band as similar to that in A1 but the powers in the theta and alpha frequency bands were relatively large as compared to those in A1 (Figure 13d). In all the three cortical sites, spindle waves, which are recognizable in sleep and/or anesthetized states (Itochev & Kubinyi, 2021; Mackenzie et al, 2004), were not apparent in both visual inspection (Figure 13b) and the power spectrum analysis (upper right inset graphs in Figure 13d) except for the rare emergence of short and small oscillatory potentials buried in lower frequency waves (arrowhead in Figure 13b) that could correspond to fragmented pentobarbital spindles (Mackenzie et al, 2004).…”

Neuromodulation via muscarinic acetylcholine pathway can facilitate distinct, complementary, and sequential roles for NREM and REM states during sleep-dependent memory consolidation

“…Thus, while the model does not incorporate more circuit-specific sleep-state features (i.e. localized modulation by other neuromodulator systems, interneuron subpopulation-specific effects, or specific network oscillations)(3, 4, 102-104), it recapitulates this more fundamental aspect of brain state regulation.…”

“…Further, we do not include sleep dependent changes in input to the network (e.g. thalamic role in formation of NREM spindles (90).…”

Automated rodent sleep spindle detector: MATLAB app using two complementary search algorithms

“…They also demonstrate enhanced spindle activity with the administration of benzodiazepines and barbiturates [13]. Moreover, the temporal correlation between rodent spindles and hippocampal ripples, which are high-frequency oscillations crucial for memory consolidation and information processing, has made rats the most extensively studied mammals in neuroscience, providing valuable insights into the intricate interplay between brain regions and their contributions to cognitive functions [14].…”

“…Rodent models are suitable for, and thus widely employed, in neuroscience research [14]. They offer unique advantages for studying conditions that are challenging or near impossible to investigate using human models.…”