As quantification of coordinated activity between neural systems became more precise, researchers began describing how different areas interacted with one another ( Boudreau, 1964 Abraham et al., 1973 Holsheimer et al., 1979 Bressler, 1984 Boeijinga and Lopes da Silva, 1989 Wróbel et al., 1994). Amplitude modulated sounds were shown to evoke 15–30 Hz responses in parts of the canine auditory cortex ( Tielen et al., 1969), and recordings from the visual cortex of dogs trained to detect sinusoidally modulated light also showed beta oscillations ( Lopes da Silva et al., 1970). Reports of beta rhythms in mammalian sensory systems extend at least as far back as the 1940s, when Adrian (1942) reported breathing- and scent-related 15–20 and 30–40 Hz rhythms in the hedgehog and rabbit olfactory bulb, hedgehog piriform cortex, and lateral olfactory tract of cats. To maintain consistency we will adopt the 15–40 Hz definition from the sensory systems literature in this review. In contrast, early hippocampal research often separated rhythms into regular slow activity (often recognized as theta) and fast rhythms, which we would now call gamma, without consistent reference to their frequency content ( Leung, 1992). Fortunately, sensory systems work has been relatively consistent with its definition of beta as an often brief, 15–40 Hz rhythm. For general descriptions of how beta fits into circuit and system-wide oscillatory dynamics (see Kay et al., 2009 Kay, 2014 Kopell et al., 2014).īefore exploring the early work on beta, we should note that beta is not always defined in the same way, and its definition has changed over time. To learn more about beta rhythms in motor systems, and how they become pathological in neurodegenerative diseases (see Stein and Bar-Gad, 2013 Singh, 2018 Barone and Rossiter, 2021). Instead, for reviews on beta rhythms in (primate) cortical information processing, we refer the reader to Spitzer and Haegens (2017) and Miller et al. Since this review will focus on sensory-cortical and hippocampal beta, as well as hippocampal beta coupling with other brain regions, we will not be reviewing all aspects of the beta rhythm. Based on these results, we will suggest that hippocampal beta is a distinctive rhythm that may have dual roles in sensory- and memory-guided behaviors. After briefly summarizing historical reports of beta, both in early sensory regions and the hippocampus, we will discuss new evidence suggesting cross-regional interactions between the hippocampus and a number of areas at beta frequencies. Thus the goal of this review is to examine and relate the literature describing beta rhythms in sensory systems to beta rhythms in hippocampal processing. Prior work had indicated that beta rhythms occurred in other early sensory systems, such as the visual and auditory systems, and work since then has reaffirmed the existence of hippocampal beta in contexts that seemingly have nothing to do with active olfaction.Īt the core of systems neuroscience is the promise of illuminating relationships between typically distinct sub-disciplines. The rhythmic coupling between these structures was strongest in the 15–40 Hz frequency band–the frequency of a classic olfactory system oscillation known as the beta rhythm. When researchers studying olfaction started recording from the hippocampus in the 1990s and 2000s they found that hippocampal activity could oscillate coherently with activity in early olfactory regions. Using this framework, we also propose circuitries that may support these processes, and experiments to test our hypothesis. After evaluating this work, we propose a framework wherein the hippocampal beta oscillation and its diverse coupling with other brain areas can support both sensory learning and memory-guided decision-making. Starting with foundational observations based largely in olfactory systems neuroscience, we review evidence suggesting beta-based activity may extend across sensory systems generally, as well as into the hippocampus and areas well known for coordinating decisions and memory-guided behaviors. In this review, we aim to strengthen the dialog between sensory systems research and learning and memory systems research by examining a 15–40 Hz oscillation known as the beta rhythm. Research into these oscillations spans brain areas, species, and disciplines, giving us common ground for discussing typically disparate fields of neuroscience. 2Department of Psychology, College of Arts and Sciences, University of Washington, Seattle, WA, United StatesĪ pillar of systems neuroscience has been the study of neural oscillations.1Graduate Program in Neuroscience, University of Washington, Seattle, WA, United States.Jesse Thomas Miles 1*, Kevan Scott Kidder 2 and Sheri J.
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