EFFECTS OF TDCS IN NEURAL MARKERS IN PEOPLE WITH MODERATE TO SEVERE TRAUMATIC BRAIN INJURY

G. Rivera¹, I. Irazzoky², P. Moya², I. Góngora²

¹Universidad de Chile, Physical Therapy Department, Neuroscience Deparment, Santiago, Chile, ²Universidad de Chile, Physical Therapy Department, Santiago, Chile

Background: Psychomotor slowness, attention-related disorders, and memory failure are among the most common complaints reported by people suffering chronically from moderate to severe traumatic brain injury (CMS-TBI). The lack of a common theoretical framework to explain this deficit has hampered the development of new therapeutic strategies for physiotherapists in clinical practice. Impairment in anticipatory control has been proposed as a central aspect of the psychomotor slowness to explain the difficulty of the subjects in implementing expected timing in the sensory-motor response. Under the predictive coding framework, the ability to anticipate events depends on the capacity to generate predictions at successive hierarchical levels and can be explored through neurophysiological correlates of prediction error signals. Analysis of event-related potentials (ERP) allows us to dissect at least three hierarchical levels of prediction error signals: the mismatch negativity (MMN; low-level), the P3a (intermediate level), and the P3b (high-level). At the same time, previous reports have shown that non-invasive brain stimulation over prefrontal areas helps improve cognitive and motor performance. We hypothesize that psychomotor slowness in CMS-TBI is related to the impairment of the normal generation of high-level top-down prediction, which is improved by an external modulation of the excitability of the frontal areas.

Purpose: To determine if people with CMS-TBI have disturbances to generate high-level top-down predictions and to explore if these disturbances are modulated by transcranial direct current stimulation (tDCS) over the left or right prefrontal cortex.

Methods: Electroencephalography (EEG) recordings were collected from 23 CMS-TBI subjects. Psychomotor slowness and other cognitive aspects were explored through a neuropsychological battery assessment and a motor reaction time task. ERPs were collected under the global-local paradigm, a task used to manipulate top-down expectations along with changes in the predictability of bottom-up information. In a single session, tDCS was applied over the left and right frontal areas. Sham tDCS was used as a control condition. Differences in the ERP were estimated through non-parametric statistical testing. In addition, multivariate pattern analysis (MVPA) was used to identify differences between stimuli that are harder to detect using conventional analyses.

Results: CMS-TBI subjects have a preserved capacity to generate top-down prediction at low hierarchical levels, indexed by the presence of MMN response. Top-down predictions at high-hierarchical levels, indexed by the P3b were hard to detect in non-parametric analysis, but through MVPA was possible to differentiate between stimuli leading to P3b (AUC = 71%, cluster-based corrected p<0.05). The tDCS over left or right PFC does not affect electrophysiological markers.

Conclusions: Subjects with CMS-TBI have preserved responses at low-hierarchical levels. Responses at high-level could be detected only through MVPA, suggesting an impairment in the generation of high-order expectations, which could explain the common deficits reported by CMS-TBI subjects. The tDCS over frontal areas does not affect the electrophysiological or behavioural measures.

Implications: Our works contribute to understanding the neurophysiological mechanisms related to psychomotor slowing, as one of the central deficits reported by CMS-TBI people. At the same time, our results allow us to explore therapeutic tools used in physiotherapy research related to the effect of tDCS.

Funding acknowledgements: Chilean National Research and Development Agency ANID, FONDECYT N° 11191161

Keywords:
TBI
EEG
tDCS

Topics:
Neurology
Disability & rehabilitation

Did this work require ethics approval? Yes

Institution: Universidad de Chile

Committee: COMITÉ DE ÉTICA DE INVESTIGACIÓN EN SERES HUMANOS

Ethics number: 169-2019