Research Articles: Behavioral/Cognitive Substantia nigra integrity correlates with sequential working memory in Parkinson’s disease https://doi.org/10.1523/JNEUROSCI.0242-21.2021 Cite as: J. Neurosci 2021; 10.1523/JNEUROSCI.0242-21.2021 Received: 1 February 2021 Revised: 6 May 2021 Accepted: 12 May 2021 This Early Release article has been peer-reviewed and accepted, but has not been through the composition and copyediting processes. The final version may differ slightly in style or formatting and will contain links to any extended data. Alerts: Sign up at www.jneurosci.org/alerts to receive customized email alerts when the fully formatted version of this article is published. Copyright © 2021 Liu et al. This is an open-access article distributed under the terms of the Creative Commons Attribution 4.0 International license, which permits unrestricted use, distribution and reproduction in any medium provided that the original work is properly attributed. 1 Research Article 2 Substantia nigra integrity correlates with sequential working 3 memory in Parkinson’s disease 4 Running title: substantia nigra & sequential memory in PD 5 Wenyue Liu 1,2, Changpeng Wang 3, Tingting He 3, Minghong Su 2,4, Yuan Lu 1, 6 Guanyu Zhang 2,4, Thomas F. Münte 5, Lirong Jin 3,*, Zheng Ye 1,6,* 7 1Institute of Neuroscience, Key Laboratory of Primate Neurobiology, Center for 8 Excellence in Brain Science and Intelligence Technology, Chinese Academy of 9 Sciences, Shanghai 200031, China 10 2University of Chinese Academy of Sciences, Beijing 100049, China 11 3Department of Neurology, Zhongshan Hospital, Fudan University, Shanghai 200032, 12 China 13 4Institute of Psychology, Chinese Academy of Sciences, Beijing 100101, China 14 5Department of Neurology, University of Lübeck, Lübeck 23538, Germany 15 6Shanghai Center for Brain Science and Brain-Inspired Intelligence Technology, 16 Shanghai 201210, China 17 18 WL, CW, and TH equally contributed to this work. 19 *Corresponding authors: 20 Zheng Ye, Institute of Neuroscience, Center for Excellence in Brain Science and 1 21 Intelligence Technology, Chinese Academy of Sciences, Yueyang Road 320, Shanghai 22 200031, China, E-mail: [email protected] 23 Lirong Jin, Department of Neurology, Zhongshan Hospital, Fenglin Road 180, 24 Shanghai 200032, China, E-mail: [email protected] 25 26 Number of figures: 3 (color) 27 Number of tables: 2 28 Number of words for Abstract (max. 250 words): 250 29 Number of words for Introduction (max. 650 words): 576 30 Number of words for Discussion (max. 1500 words): 1394 31 32 Conflict of interest 33 The authors declare no competing financial interests. 34 Acknowledgments 35 This work was supported by the National Natural Science Foundation of China 36 (31961133025, 31771216) and the Shanghai Municipal Science and Technology 37 Major Project (2018SHZDZX05). Lirong Jin was supported by the Shanghai 38 Municipal Science and Technology Commission (2018ZR1406500). We would like to 39 thank Dr. Jian Wang for her comments on data analysis and Biman Xu for her 40 assistance in data acquisition. 41 2 43 Abstract 44 Maintaining and manipulating sequences online is essential for daily activities such as 45 scheduling a day. In Parkinson’s disease (PD), sequential working memory deficits 46 have been associated with altered regional activation and functional connectivity in 47 the basal ganglia. This study demonstrates that the substantia nigra (SN) integrity 48 correlated with basal ganglia function and sequencing performance in 29 patients with 49 PD (17 women) and 29 healthy controls (HC, 18 women). In neuromelanin-sensitive 50 structural MRI, PD patients showed smaller SN than HC. In a digit ordering task with 51 functional MRI, participants either recalled sequential digits in the original order 52 (‘pure recall’) or rearranged the digits and recalled the new sequence (‘reorder & 53 recall’). PD patients performed less accurately than HC, accompanied by the caudate 54 and pallidal hypo-activation, subthalamic hyper-activation, and weakened functional 55 connectivity between the bilateral SN and all three basal ganglia regions. PD patients 56 with larger SN tended to exhibit smaller ordering-related accuracy costs (‘reorder & 57 recall’ versus ‘pure recall’). This effect was fully mediated by the ordering-related 58 caudate activation. Unlike HC, the ordering-related accuracy cost correlated with the 59 ordering-related caudate activation but not subthalamic activation in PD. Moreover, 60 the ordering-related caudate activation correlated with the SN area but not the daily 61 dose of D2/3 receptor agonists. In PD, the daily dose of D2/3 receptor agonists 62 correlated with the ordering-related subthalamic activation, which was not related to 63 the accuracy cost. The findings suggest that damage to the SN may lead to sequential 4 64 working memory deficits in PD, mediated by basal ganglia dysfunction. 65 Keywords: Parkinson's disease; substantia nigra; basal ganglia; sequential working 66 memory; neuromelanin-sensitive MRI; functional MRI 67 Significance 68 Liu et al. demonstrate that damage to the substantia nigra (SN) correlates with basal 69 ganglia dysfunction and poor sequencing performance in Parkinson’s disease (PD). In 70 neuromelanin-sensitive MRI, PD showed smaller SN than healthy controls. In a digit 71 ordering task with functional MRI, PD’s lower task accuracy was accompanied by the 72 caudate and pallidal hypo-activation, subthalamic hyper-activation, and weakened 73 functional connectivity between the SN and basal ganglia. PD with larger SN 74 exhibited greater ordering-related caudate activation and lower ordering-related 75 accuracy cost when sequencing digits. PD with more daily exposure to D2/3 receptor 76 agonists exhibited greater ordering-related subthalamic activation, which did not 77 reduce accuracy cost. It suggests that the SN may affect sequencing performance by 78 regulating the task-dependent caudate activation in PD. 79 80 5 81 1. Introduction 82 The ability to maintain and manipulate sequential information online is essential for a 83 broad spectrum of daily activities (e.g., scheduling a day). In Parkinson’s disease (PD), 84 sequential working memory deficits can lead to difficulties in sorting words and 85 numbers (Cooper et al., 1991; Gabrieli et al., 1996), organizing sequential steps to 86 achieve goals (Owen, 1997; West et al., 1998; Sullivan et al., 2009), and 87 understanding the relationship between events that are not stated in the order they 88 occurred (Natsopoulos et al., 1991; Al-Khaled et al., 2012). We have linked PD’s poor 89 sequencing performance with altered regional activation and functional connectivity 90 in the basal ganglia (Ye et al., 2021). In this study, we further investigate whether 91 damage to the substantia nigra (SN) could contribute to the basal ganglia’s functional 92 changes using neuromelanin-sensitive structural as well as functional MRI. 93 Recently we described a neural system for sequential working memory, comprising 94 the lateral prefrontal cortex, posterior parietal cortex, caudate nucleus, globus pallidus, 95 subthalamic nucleus, and thalamus (Ye et al., 2020). Both PD and normal aging can 96 compromise this neural system but in different manners. The age effect led to 97 prefrontal and parietal hyper-activation and a weakened psychophysiological 98 interaction between the prefrontal/parietal regions and the supplementary motor area 99 (Ye et al., 2020). In contrast, the disease effect was manifested as subthalamic and 100 pallidal hyper-activation and weakened functional connectivity between the 101 subthalamic nucleus and striatum (Ye et al., 2021). 6 102 Cognitive decline in early PD may correlate with the spread of misfolded α-synuclein 103 (Braak et al., 2006), which hits the locus coeruleus (LC) in stage 2 and the SN in stage 104 3 of the disease. We hypothesize that the basal ganglia's functional changes during 105 sequential working memory correlate with the degree of SN integrity. To test this 106 hypothesis, we measured the SN integrity in vivo using neuromelanin-sensitive MRI. 107 Neuromelanin is a by-product of catecholamine synthesis, existing in SN dopamine 108 neurons and LC noradrenaline neurons (Zecca et al., 2001; Fedorow et al., 2005). In 109 PD, MRI signals of the neuromelanin are remarkably diminished in the SN and LC 110 (Sasaki et al., 2006; Martin-Bastida et al., 2017; Wang et al., 2018), consistent with 111 the loss of dopamine and noradrenaline neurons in these nuclei (Isaias et al., 2016; Ito 112 et al., 2017). It raises the question whether changes in SN integrity might impact 113 neural processes of sequential working memory. 114 Therefore, fMRI was combined with a computerized digit ordering task (Fig.1A) that 115 highlighted the flexible manipulation of sequences by contrasting ‘reordering & recall’ 116 with ‘pure recall’ trials. In PD, sequence manipulation is often impaired even though 117 sequence maintenance is preserved (Ma et al., 2019). In ‘pure recall’ trials, 118 participants recalled a sequence of digits in the order they had been presented. In 119 ‘reorder & recall’ trials, they had to rearrange the digits in ascending order and recall 120 the new sequence. First, we sought to replicate group differences in task accuracy (Ye 121 et al., 2021) and SN integrity (Sasaki et al., 2006; Wang et al., 2018). Second, we 122 wanted to detect whether the basal ganglia exhibit altered regional activation or 7 123 functional connectivity with the SN. Third, we aimed to examine whether altered 124 basal ganglia activation or functional connectivity mediates SN’s effect on task 125 accuracy. In particular, we asked whether the ordering-related accuracy cost correlates 126 with the basal ganglia activation or functional connectivity with the SN 127 (brain-behavior relationship) and whether the ordering-related basal ganglia activation 128 correlates with the SN integrity or daily dose of dopaminergic drugs 129 (structure-function relationship). 130 Fig.1 131 132 2. Materials and Methods 8 133 This study was approved by the ethics committee of the Chinese Academy of 134 Sciences Institute of Neuroscience, according to the Declaration of Helsinki.