Neuroimaging studies of musicians and musicianship is an important focus of inquiry that began to emerge robustly in the early 2000s (Pantev et al. 2001, Munte et al. 2002, Bangert et al. 2006, Jäncke 2009, Elmer & Jäncke 2018) [1–5]. Recent work on musicians, especially diffusion tensor imaging (DTI) analysis of white matter tracts, has contextualized imaging analysis within the framework of aging and building cognitive reserve (e.g. Halwani et al. 2011, Oechslin et al. 2010, Andrews et al. 2021) [6–8].
Neuroimaging research focusing on professional musicians can be categorized into the following main topics: (1) the relationship of musicianship and neuroplasticity (Jäncke 2009; Munte et al., 2002) [4, 2], (2) neuroanatomical correlates of musicianship (Pantev et al. 2001, Bermudez et al. 2009) [1, 9] (3) enhanced encoding of vowels and speech in professional musicians (Weiss and Bidelman, 2015) [10]., (4) timbre-specific auditory cortical representations in musicians (Kuhnis et al. 2013) [11], (5) shared networks for auditory and motor processing in professional musicians (Bangert et al. 2006) [3], and (6) brainstem recordings of speech sounds in musicians (Weiss and Bidelman, 2015) [10]. The above studies have been investigated using various functional and structural magnetic resonance imaging techniques (MRI). Resting-state functional MRI (rfMRI) focusing on musicians began to emerge more recently and have been limited to studies of improvisation (Bengtsson et al. 2007, Berkowitz, Ansari et al. 2008, 2010, Lopata et al. 2017, Rosen et al. 2016 for some examples) [12–16], different types of musical training (Belden et al. 2020) [17] and more general musical creativity (Bashwiner et al. 2020) [18]. These studies apply regions of interest (ROI) seed-based analysis approaches.
There are a range of terms used in the published literature to characterize different types of brain reserve. Neurological (brain) reserve, one of the earliest terms proposed (Valenzuela et al. 2006) [19] is generally considered to be more biologically and genetically based, and includes different definitions, including:
(1) “The neurological brain reserve hypothesis proposes that individuals generally differ in the numbers of neurons and synapses available to be lost before clinical symptoms emerge” (Stern, 2012) [20].
(2) “Brain reserve refers to ‘passive’ factors (e.g., brain volume, synapse count) that confer a particular capacity to endure neuropathological processes until a critical threshold is reached, after which cognitive and functional impairments are expressed” (Guzmán-Vélez, 2015) [21].
In contrast, cognitive reserve, also called behavioral brain reserve, is acquired through specific sensory–motor activities that span across the life cycle (including but not restricted to musicianship and bilingualism). This type of cognitive brain reserve is considered “resilience to neural insult” and strategies that strengthen alternative FNs across the life cycle can improve tolerance of atrophy (Bialystok, 2007) [22]. Moreover, higher cognitive reserve should require more structural decline in order for symptoms to manifest (Gold et al. 2013) [23]. For more discussion on cognitive reserve, see Craik et al., 2010; Andrews et al., 2013, 2021; Andrews, 2014; and de Bot, 2009 [24, 25, 8, 26, 27].
In the current work, we will examine white matter (WM) integrity and in particular fractional anisotropy (FA) values in healthy subjects who are high proficiency musicians and in age and educational matched non-musician controls. Because this is a direct extension of our original analysis (Andrews et al. 2021 [8]) where only high proficiency, lifelong musicians were analyzed, some of the central points from the 2021 publication are included in this short discussion.
The general consensus in the published research on the different kinds of cognitive brain reserve notes specific trends in functional reorganization of functional connectivity and neural networks across modalities, as well as enhancement of the generation of neuronal, dendritic and synaptic connections while also recognizing the lack of understanding of the mechanisms for these trends. Different research favors different neural regions. Grundy et al. (2017) argue in favor of a shift to subcortical/posterior region-based networks in bilinguals from more frontal regions in monolinguals [28]. Abutalebi et al. (2015) focus on increased gray matter (GM) in bilingualism as an example of cognitive reserve and potential protective effects in aging [29, 30].
The focus of the current study is the notion that cognitive brain reserve not only may play a role in delaying the appearance of symptoms of certain pathologies, but it also may play a role in healthy subjects. Our research focuses on lifelong musicians and potential effects of musicianship on subcortical WM matter fiber tracts. This follow-up study to our 2021 work, which includes an age and education matched cohort of controls, does not include GM volume changes, which is also the subject of current research (cf. Pliatsikas et al. 2015) [31].
It has been shown in multiple studies that WM integrity decreases in normal aging (cf. Tang et al. 1997, Giorgio A, Santelli L, Tomassini V, et al. 2010, Westlye et al. 2010, Billiet T, Vandenbulcke M, Madler B, et al. 2015, Rathee et al. 2016) [32–36]. For our work, research on cognitive reserve, interactions between bilingualism and musicianship, and studies specifically focusing on musicianship provide the foundation for our research question and hypotheses. The emerging picture suggests that the process of WM integrity loss can be slowed down or changed by lifelong bilingualism and musicianship.
Our first paper published on DTI study of lifelong musicianship (Andrews et al. 2021) hypothesized that there will be an increase in WM integrity in certain subcortical fiber tracts in lifelong musicians, and that this increase will be reflected bilaterally in FA values for the bilateral superior longitudinal fasciculus (SLF) and the uncinate fasciculus (UF) – 2 specific WM tracts shown to be relevant in musicianship [8]. We also hypothesized that the bilateral SS, which includes the IFOF (a tract important in bilingualism), may not show the same effects. This follow-up study considers lifelong musicianship with age-matched non-musician controls with an age span from 20 to 67 years. The central hypothesis states that age-matched non-musician controls will not show the increases in WM integrity across the age span found in lifelong musicians for bilateral SLF and bilateral UF.