3. Brain Stimulation

Brain Stimulation

Research activities

The overarching goal of the lab is to study the temporal dynamics and the compensatory physiological and behavioral responses of the visual system using noninvasive brain stimulation coupled with functional imaging and behavioral psychophysical testing.

The work in our research lab focuses on the study of attentional functions in the healthy and diseased brain. Specifically, we have performed studies of inter- and intra-hemispheric connectivity, its impairment in stroke and its recovery after noninvasive brain stimulation as therapeutic treatment. In addition to brain stimulation and behavioral measures, we perform MRI analysis of both intact and neurologically impaired subjects. Finally, we apply noninvasive brain stimulation either for focally perturbing or enhancing brain functions in healthy subjects.

Collaborations

  • Emily Grossman
  • Duje Tadin
  • Krystel Huxlin
  • Aaron Seitz
  • Sara Mednick
  • Clayton Hickey
  • Alex Holcombe
  • George Alvarez
  • Anna Montagnini
  • Alfonso Caramazza

Projects

Time perception: how does the visual system interpret a coherent, integrated percept of motion in dynamic visual scenes?

The main question we ask is: how does the visual system analyze the complex visual environments? What happens when these processes go away after cortical strokes? As part of our studies, we examine neurological patients affected by stroke involving cortical areas. We have discovered that unilateral right parietal stroke patients show a severe visual deficit in a simple apparent motion task, but are unaffected in low- level (smooth) motion tasks. Based on these and other findings, we proposed a new theory: that visual relative timing, and perhaps relative timing in general, is a specialized function of the right inferior parietal lobe. In a series of papers, we hypothesized that relative timing impairments could broadly underlie many of the perceptual and attentional deficits in patients with parietal lesions.

Sustained attention: perturb-and- measure the neurophysiological substrates of visual attention

Another function of the parietal lobe we are interested in is attentional tracking. Our work has provided direct evidence that the two parietal lobes compete with each other during sustained attention. In a set of experiments, we used combined fMRI and rTMS to study the cortical networks involved in attentional tracking. We used 1-Hz rTMS over the parietal cortex to study the dynamic interplay across cortical attention networks in the brain of normal subjects. Low frequency rTMS temporarily mimics the behavioral effects of parietal stroke, and in our study, we compared brain activity after active versus sham stimulation using fMRI. Our studies demonstrated the feasibility of using fMRI immediately following a single session of rTMS to detect temporary changes in neural activity throughout the neural network involved in sustained attention. The data also suggest the intriguing possibility that rTMS could be used to treat and improve attentional functions in unilateral stroke patients.

Restoring attentional functions in parietal stroke patients

Our combined rTMS-fMRI experiments have led the lab work into new and exciting directions. Our findings suggested that the two cortical hemispheres inhibit one another during normal brain function. It follows that if one hemisphere is inactivated or damaged, its reduced activity could disinhibit the opposite (healthy) hemisphere, leading to abnormally increased activity in the healthy hemisphere that in turn overly-inhibits the lesioned hemisphere. This hypothesis suggested a strategy to treat attentional deficits: reduce the over-activity of the healthy, contra-lesional hemisphere by applying inhibitory rTMS, thus reducing the excess inhibition of the lesioned hemisphere, leading to improved attentional function. We have used rTMS as a rehabilitation technique in patients affected by visual neglect and extinction. Our studies established a proof-of-principle for using neuromodulation as a tool to boost cognitive and motor functions.

Biological motion: how the visual system interprets complex visual motion?

In the laboratory, we have explored the cortical mechanisms involved in the integration of visual information across space and time. We have addressed the question of how the visual system interprets the integrated form and motion of patterns of point-lights that describe bodily forms, so-called biological motion. We demonstrated that inhibitory rTMS over a visual associative area (the superior temporal sulcus) in healthy subjects impaired biological motion perception. Finally, we have used rTMS to examine the visual cortical mechanisms responsible for actively suppressing irrelevant information in the background to enhance processing of relevant foreground objects. It had been previously found that this function is less efficient in the elderly and in certain psychiatric conditions, such as depression and schizophrenia. Our results demonstrated the middle temporal visual area (MT) plays a fundamental role in visual integration as well as in other functions.

Facilities

The lab is equipped with: a) three transcranial magnetic stimulations (single pulse and repetitive) (TMS, Magstim Rapid 2 100Hz); b) high-density EEG recording system with concurrent frameless stereotaxy-guided TMS (NeuroConn); c) frameless stereotactic system (Brainsight, Rogue, Inc.). d) three transcranial electrical stimulation devices (tES, NeuroConn). e) several computers having the necessary software to allow data entry and documentation, statistical analysis, graphical display of the results, and image processing and analysis.

Selected Publications

Members

Sara Agosta
PostDoc

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Florian Herpich
PhD student

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Federica Conto
PhD student

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Danielle Parrot
PhD student

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Grace Edwards
PostDoc

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Denise Magnago
Research assistant

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Principal investigator

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Lorella Battelli

I am interested in dynamic vision and motion perception. My previous research has focused on the effects that a brain lesion to the associative visual areas has upon the ability to discriminate and integrate visual events. While this neuropsychological work has suggested a hypothesis about the role of the parietal cortex, the general approach is severely limited. For example, brain lesions caused by a stroke usually extend beyond the area of interest in the study, and a damaged brain may have undergone months or years of reorganization and adopted compensatory strategies. Moreover lesion studies may reveal the capability of other cortical areas in the absence of the damaged cortical tissue and not the true functions of that specific area. For these and other reasons, I am now using the virtual-lesion methodology applying TMS to the visual cortex of healthy volunteers and producing reversible functional disruption. TMS has excellent temporal resolution, and can be spatially confined, and this has been useful in mimicking selective brain lesions.