Even with effective anti-retroviral therapy, patients infected with the Human Immunodeficiency Virus (HIV) sustain central nervous system damage. Whether these problems can be mainly attributed to the disease, its treatments, or the body\u2019s immune responses is still being debated, but detecting these changes early and reliably is difficult.<\/p>\n
Findings from a new study<\/a> published in Clinical Neurophysiology<\/em>, involving a collaborative effort between Dartmouth\u2019s Geisel School of Medicine and the Auditory Neuroscience Laboratory at Northwestern University<\/a>, are shedding further light on how the brain\u2019s auditory system may provide a window into how the brain is affected by HIV.<\/p>\n \u201cWe\u2019ve been performing a variety of hearing tests on an established cohort of HIV-positive patients in Dar es Salaam, Tanzania,\u201d says Jay Buckey, Jr., MD, a professor of medicine at Geisel who co-led the study. \u201cInitially, we thought we\u2019d find that HIV affects the ear, but what seems to be affected is the brain\u2019s ability to process sound.\u201d<\/p>\n To test this hypothesis, the researchers used what\u2019s called a speech-evoked frequency-following response (FFR). In this test, brain waves are recorded from scalp electrodes (as in an electroencephalogram) while sounds common to everyday speech, like \u201cba,\u201d \u201cda,\u201d or \u201cga,\u201d are played into the ear. This offers an objective, non-invasive way to record brain waves and assess the brain\u2019s auditory functions.<\/p>\n \u201cThere are many acoustic ingredients in speech, such as pitch, timing, harmonics, and phrase,\u201d says Nina Kraus, PhD, Hugh Knowles Professor of Communication Sciences and Neurobiology at Northwestern, who co-led the study with Buckey. \u201cThe FFR enables us to play speech sounds into the ear of study participants and figure out how good a job the brain is doing processing these different acoustic ingredients.\u201d<\/p>\n When comparing the FFR results of 68 HIV-positive adults to 59 HIV-negative adults, the investigators found that the auditory-neurophysiological responses to certain speech cues were disrupted in HIV-positive adults, even though they performed normally on hearing tests\u2014confirming that these hearing difficulties are grounded in the central nervous system.<\/p>\n \u201cWhen the brain processes sound, it\u2019s not like a volume knob where all of the acoustic ingredients are either processed well or poorly,\u201d Kraus explains. \u201cWith the FFR, we\u2019re able to see which aspects of auditory processing are affected or diminished and ask, \u2018Is there a specific neural signature that aligns itself with HIV?\u2019\u201d<\/p>\n That\u2019s why the researchers envision the FFR as a viable tool for further understanding not only the mechanisms of brain dysfunction associated with HIV, but also other disorders that affect the brain such as concussion, Alzheimer\u2019s disease, and the Zika virus infection.<\/p>\n \u201cTypically, if you want to assess cognitive function, you\u2019re going to do things like have people do math problems, remember a list of words, work on some sort of puzzle or task, or do a drawing,\u201d says Buckey. \u201cIt requires people who are trained in doing this kind of testing, and the tests may be fairly specific to the language people speak and the culture they come from.<\/p>\n \u201cWhat\u2019s significant about our results is that the test doesn\u2019t require any actions on the patient\u2019s part; it\u2019s recorded passively\u2014subjects can even sleep or watch a movie,\u201d he says. \u201cWe think the FFR holds a lot of promise as a way to assess the brain easily and objectively.\u201d<\/p>\n Founded in 1797, the\u00a0Geisel School of Medicine at Dartmouth <\/strong>strives to improve the lives of the communities it serves through excellence in learning, discovery, and healing. The Geisel School of Medicine is renowned for its leadership in medical education, healthcare policy and delivery science, biomedical research, global health, and in creating innovations that improve lives worldwide. As one of America\u2019s leading medical schools, Dartmouth\u2019s Geisel School of Medicine is committed to training new generations of diverse leaders who will help solve our most vexing challenges in healthcare.<\/p>\n Watch: Discovery@Dartmouth Video\u00a0with Jay Buckey, MD<\/strong><\/p>\n