Unveiling top-down modulation of Hand Blink Reflex through functional Near-Infrared Spectroscopy

2058 

Abstract Submission 

Monica Biggio¹, Costanza Iester², Ambra Bisio³, Sabrina Brigadoi⁴, Simone Cutini⁴, Laura Bonzano², Marco Bove⁵

¹Università degli studi di Genova, Genova, Italy, ²Department of Neuroscience, DINOGMI, University of Genoa, Genoa, Italy, Genova, Italy, ³DIMES, Section of Human Physiology, University of Genoa, Genova, Liguria, Italy, Genova, Italy, ⁴Department of Developmental Psychology, University of Padova, Padova, Italy, Padova, Italy, ⁵DIMES, University of Genoa, Genova, Italy

Monica Biggio  
Università degli studi di Genova
Genova, Italy

Costanza Iester  
Department of Neuroscience, DINOGMI, University of Genoa, Genoa, Italy
Genova, Italy

Ambra Bisio  
DIMES, Section of Human Physiology, University of Genoa, Genova, Liguria, Italy
Genova, Italy

Sabrina Brigadoi  
Department of Developmental Psychology, University of Padova, Padova, Italy
Padova, Italy

Simone Cutini  
Department of Developmental Psychology, University of Padova, Padova, Italy
Padova, Italy

Laura Bonzano  
Department of Neuroscience, DINOGMI, University of Genoa, Genoa, Italy
Genova, Italy

Marco Bove  
DIMES, University of Genoa
Genova, Italy

Hand Blink Reflex (HBR) is a subcortical defensive reflex evoked by the stimulation of the median nerve at the wrist1. Its intensity increases when the stimulated hand is placed near the face, inside the boundaries of the defensive peripersonal space of the face (DPPS). Therefore, along with the brainstem circuit mediating the blink reflex, a top-down modulation of HBR has been proposed, particularly in ventral intraparietal (VIP) and polysensory zone (PZ), areas related to DPPS representation. Here we aim to verify this hypothesis for the first time with the use of functional Near-Infrared Spectroscopy (fNIRS).

Twenty-eight healthy participants (Age: 23 ± 0.57 years) were recruited for a session of non-invasive electromyography (EMG). HBR was evoked by administering transcutaneous electrical stimuli (ES) to the right median nerve of the wrist in two target positions with respect to the face: i.e., when the elbow angle was: 10◦ less than the maximal arm extension (FAR position) and 10◦ more than the maximal elbow flexion (NEAR position). Stimulus intensity was adjusted to elicit in each participant clear HBR responses (mean stimulus intensity: 7mA ± 0.52). Reflex responses were recorded bilaterally from orbicularis oculi muscles. Fifteen HBR responses were recorded from both positions for a total of thirty trials. Simultaneously, we performed an fNIRS acquisition to investigate the cortical activity immediately preceding the ES (PRE-STIMULUS_) and immediately after the ES, containing the HBR response (STIMULUS_) in the two positions. Optodes were arranged resulting in a total of 44 standard channels (3cm) and 8 short-separation channels. For each participant the fNIRS signal was pre-processed: channels with low signal–to–noise ratio were discarded; intensity data were converted to attenuation changes and motion artifacts were corrected by applying spline2 and wavelet3 motion correction techniques; a band-pass filter (0.01-3 Hz) was applied, and the mean hemodynamic response for each task block, participant and channel was recovered using a general linear model approach. This also led to removing physiological noise by regressing the most correlated short-separation channel from each standard channel. Then, we averaged channels belonging to the same Brodmann's area (BA) obtaining 11 regions of interest. The mean values of Oxy-hemoglobin (HbO) responses were computed for all BAs in an interval of 10 seconds before the stimulus onset in PRE-STIMULUS_ and after the stimulus onset in STIMULUS_ condition.

Participants showed a significantly increased HBR response when evoked in NEAR, with respect to FAR (Fig 1), as shown in previous literature1,4.
PRE-STIMULUS analysis showed a significant effect of POSITION, i.e. an overall lower cortical activity in PRE-STIMULUS_FAR with respect to PRE-STIMULUS_NEAR. Also, a significant POSITION * BA interaction indicated a greater activity in BA4 and 3 in PRE-STIMULUS_NEAR. In STIMULUS condition, significant effects of BA and HEMISPHERE were found, indicating greater activation of BA4 and 3, in particular in the left hemisphere, and a significant deactivation of BA44 in the NEAR with respect to the FAR condition (Fig 2).

Stimulus preparation varies according to arm position, particularly in somatosensory and motor areas, predisposing the system to an increased response, or conversely deactivating the system when a response is not required, in a "energy saving" mechanism when the stimulus is implicitly perceived as not risky4. These areas remain active after stimulus reception, with no significant difference between positions. After the stimulus BA44, corresponding to the inferior frontal Gyrus, appears to be deactivated. BA44 has been associated with the judgement of the position of visual and somatosensory stimuli relative to their body midline5, and also with risk assessment and aversion6. At present it has not been possible to confirm the involvement of the VIP-PZ circuit in HBR modulation.

Motor Behavior Other ¹

NIRS ²

Cortex

ELECTROPHYSIOLOGY

Near Infra-Red Spectroscopy (NIRS)

Nerves

Peripheral Nerve