Neuroimaging: “Kodak Moments” for Essential Tremor

What if you had a camera that could take photos of your brain when it’s active? Would you expect to see different parts of your brain “light up” when you’re doing various activities? For example, does your brain use different areas for paying bills, playing tennis, and talking to the vet about your dog’s limp?

Using imaging to understand essential tremor

Essential tremor (ET) is the most common movement disorder, yet no one has been able to unravel the mystery of what causes it. A great deal of research has identified certain structures or areas of the brain that seem to be involved in tremor activity, and the pathway from where it seems to originate, through the brain, and out to the affected body part. This pathway is called the tremor network. According to Sharifi et al. (2014), “The exact mechanisms and possible structural or functional changes within the tremor network are not fully understood.”¹ However, at the risk of oversimplifying, the predominant theories hold that malfunctioning signals in the part of the brain called the cerebellum are the root source of tremors. These signals are transmitted along the tremor pathway to the thalamus (or part of the thalamus), which then acts as a relay station to forward these signals to the motor cortex in the forebrain.

Imaging of the brain, or neuroimaging, is an incredible addition to the science behind tremors. It has applications for studying tremors related to ET, Parkinson’s disease and parkinsonism. Neuroimaging helps us understand how the tremor network, and the key structures within that network, differs from the same pathway in persons who do not have ET (in clinical studies, non-ET participants are called controls or the control group).

Types of neuroimaging

There are two primary imaging technologies that are used for brain imaging of ET patients: Magnetic resonance imaging (MRI) and positron emission tomography (PET) scans that use radiotracers (radioactive isotopes). Each of these types has subtypes that have a particular refinement.

MRI subtypes

• Voxel-based morphometry (VBM) distinguished and quantifies white matter from grey matter
• Diffusion-weighted imaging (DWI) and diffusion-tensor imaging (DTI) can be used to “map” messaging circuits in the brain
• Magnetic resonance spectroscopy (MRS) evaluates the metabolic function of brain cells, that is, biochemical processes to rule out a neurodegenerative condition
• T2-weighted contrasts (T2 MRI) can assess brain iron concentrations, which have been linked with neurodegenerative disorders
• Functional MRI (fMRI) can detect blood oxygen levels during brain tasks, highlighting which areas are activated. For example, in one study of 12 ET patients and 15 controls, the ET patients showed activation of two areas during tremor, while these areas did not activate in the control participants when they were asked to mimic tremors.

PET subtypes

• PET scans use photon-emitting radiotracers that highlight metabolic processes in cells as a way to distinguish normal tissues from abnormal ones. PET scans give better image contrast and resolution but are more expensive than SPECT.
• Single-photon PET (SPECT) have the same purpose as PET scans but use gamma-emitting radiotracers.

What neuroimaging reveals about ET

For the most part, neuroimaging studies confirm unusual structural and neuronal activity in the cerebellum, and secondarily in the thalamus. Sharifi et al. concluded, “Functional imaging studies that provide insights in regional cerebral blood flow and metabolism point to the cerebello-thalamo-cortical outflow pathways, with cerebellar involvement as the most consistent finding.”² In addition, structural imaging suggests brain deterioration in certain types of ET, which is increasingly understood as a family of tremor disorders, not just a single universal disorder. See my blog on the GABA hypothesis.

MRgFUS to control medication-resistant tremors

At Sperling Neurosurgery Associates, we offer MRI-guided Focused Ultrasound using the Neuravive system. This noninvasive, one-time outpatient procedure is safe, effective, and durably controls tremors by ablating the VIM nucleus in the thalamus. Thanks to the imaging power of MRI, this tiny center deep in the brain can be accurately mapped, targeted, and monitored during treatment.

Visit our website for more information on the treatment, and how to contact us.

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¹Sharifi S, Nederveen AJ, Booij J, van Rootselaara, AF. Neuroimaging essentials in essential tremor: A systematic review. Neuroimage Clin. 2014; 5: 217–231.
² Ibid.