Supplementary Information
Low level mercury, omega-3 index and neurobehavioral outcomes in an adult U.S. coastal population
Caterina Vacchi-Suzzi1, Roxanne Karimi2, Danielle Kruse6, Susan M. Silbernagel5, Keith E. Levine3,Diane S. Rohlman4, Jaymie R. Meliker1*
1Program in Public Health,Department of Preventive Medicine, Stony Brook University, NY, 11794, USA
2 School of Marine and Atmospheric Sciences,Stony Brook University, Stony Brook, NY, 11794, USA
3Trace Inorganics Department, Technologies for Industry and the Environment,RTIInternational, Research Triangle Park, NC, 27709, USA
4 Occupational and Environmental Health, University of Iowa, Iowa City, IA, 52242, USA; Oregon Institute for Occupational Health Sciences, Oregon Health & Science University, Portland, OR 97239, USA
5 Division of Allergy and Infectious Diseases,Department of Medicine, University of Washington, Seattle, WA, 98195, USA
6School of Medicine, Stony Brook University, NY 11794, USA
*Corresponding author: Jaymie R. Meliker, Ph. D.,
Supplementary Material and Methods
Description of the Neurobehavioral Tests
The Symbol-Digit test [1] presents a matrix at the top of the screen that pairs nine unique symbols with the numbers one through nine. A second matrix that contains only the symbols is shown below. Participants are asked to press the corresponding number button for each symbol. Latencies for each button press are recorded.
The Tapping test instructs the participant to press a button as many times as they can for a period of time (e.g., twenty seconds). Performance using each hand can be tested, as well as an alternation trial in which participants are instructed to tap sequentially with the left and then the right hand (then left, then right, and so on) for a period of time. The number of taps is recorded for all trials.
In the Simple Reaction Time Test, participants are asked to press a button as fast as they can when a square appears on the screen. Latencies for each button press are recorded.
The Continuous Performance Test measures attention. Stimuli are sequentially presented on the screen every 50 ms when the target stimulus (plus sign followed by a circle) is presented, the participant responds by pressing a button. Three hundred stimuli are presented; 20% of them are target stimuli. The percent correct, incorrect (false alarms and omissions), and response latencies are recorded.
The Match-to-Sample test measures visual memory. Participants are shown a 10x10 matrix with certain squares filled in, after a variable delay (1, 8 or 16 seconds) they are instructed to choose the correct pattern from among 3 choices. The number correct as well as the latency required to make a correct response is recorded.
The Digit Span Test sequentially presents a series of numbers on the screen. The participant is instructed to reproduce the series of numbers by pressing the nine numbered buttons in the same sequence (forward), or, in the second part of the test, in the reverse sequence (reverse). Number sequences are presented in increasing length starting from three numbers. The test is terminated when a participant fails two consecutive trials with the same number of digits, or when they completed a span of nine digits correctly.
The Reversal Learning Test presents shapes one at a time until the participant learns the correct response e.g., press 3 or press 7). Once a performance criterion is reached (e.g., 5 out of 6) the correct response switches. The test measures how long the participant takes to learn the original pattern of responses and then how long to learn the switched responses. This task is similar to a switching task like the Wisconsin Sorting Task.
Description of the Self-reported Health Questionnaire
During the study visit, LISS study participants answered 59 questions about their general health conditions and specific diagnoses. For investigating the symptoms inTable 5, participantswho answered either“Always” or “Usually”to the following questions were considered to be experiencing the symptoms described in the question:
- Fatigue: “Over the past year, how often have you felt tired or had little energy”.
Answers: 1, Always | 2, Usually | 3, Sometimes | 4, Rarely | 5, Never | 6, Don't know / Not sure
- Hg-related symptoms (either of these: “Over the past year, how often have you felt a loss of balance or coordination?”, “Over the past year, have you experienced numbness or tingling around the mouth?” and “Over the past year, how often have you had trouble concentrating on things at home or at work (for example, reading the newspaper)?”.
Answers: 1, Always | 2, Usually | 3, Sometimes | 4, Rarely | 5, Never | 6, Don't know / Not sure
References to Supplementary Material and Methods
1. Smith A (1968) SDMT: A neuropsychological test for economic screening. Hearing Disorders 3:83-91
Supplementary Results
Supplementary Table 1: Test completion rates
Testa / Completion criteria / Low Hg(<5.8 µg/L) / Elevated Hg
(>5.8 µg/L)
Digit Span Forward / ≥ 1 completed task / 98% (121/123) / 100% (76/76)
Digit Span Reverse / ≥1 completed task / 98% (121/123) / 95% (72/76)
Symbol Digit / < 35 errors / 98% (120/123) / 100% (76/76)
Simple Reaction Time / < 14 errors / 96% (118/123) / 97% (74/76)
Continuous Performance / ≥ 225 trials / 99% (122/123) / 100% (76/76)
Reversal Learning / ≥ 1 correct trial / 95% (117/123) / 100% (76/76)
a Tapping (Dominant and Non-dominant) and Match-to-Sample had no completion criteria.