Magnetic field compensation coil design for magnetoencephalography

While optically pumped magnetometers (OPMs) can be attached to the head of a person and allow for highly sensitive recordings of the human magnetoencephalogram (MEG), they are mostly limited to an operational range of approximately 5 nT. Consequently, even inside a magnetically shielded room (MSR), movements in the remnant magnetic field disable the OPMs. Active suppression of the remnant field utilizing compensation coils is therefore essential. We propose 8 compensation coils on 5 sides of a cube with a side length of approximately 2 m which were optimized for operation inside an MSR. Compared to previously built bi-planar compensation coils, the coils proposed in this report are more complex in geometry and achieved smaller errors for simulated compensation fields. The proposed coils will allow for larger head movements or smaller movement artifacts in future MEG experiments compared to existing coils.

Magnetic Field Compensation Coil Design for Magnetoencephalography

While optically pumped magnetometers (OPMs) can be attached to the head of a person and allow for highly sensitive recordings of the human magnetoencephalogram (MEG), they are mostly limited to an operational range of approximately ±5 nT. Consequently, even inside a magnetically shielded room (MSR), movements in the remnant magnetic field disable the OPMs. Active suppression of the remnant field utilizing compensation coils is therefore essential. We propose 8 compensation coils on 5 sides of a cube with a side length of approximately 2 m which were optimized for operation inside an MSR. Compared to previously built bi-planar compensation coils, the coils proposed in this report are more complex in geometry and achieved 10 times smaller errors for simulated compensation fields. The proposed coils will allow for larger head movements or smaller movement artifacts in future MEG experiments compared to existing coils.

Active suppression prevents the return of threat memory in humans

Unbidden distressing memories inflict serious damage on mental health. Extant research highlights the importance of associative learning in modulating aversive memory. We report that conscious active suppression eliminates learned fear responses independent of memory triggers and is related to individual difference in thought control ability; in contrast, thought diversion only reduces cue-specific fear response. These results suggest potential avenues for treatment of persistent maladaptive memories by engaging declarative mnemonic control mechanisms.

Active Suppression of Piezoelectric Ringing in Pockels Cells for Laser Cavity Application

Pockels cells used as electro-optical modulators in high-power high-repetition lasers suffer from piezoelectric ringing phenomenon due to piezoelectric properties of the crystals. A new method for active suppression of the piezoelectric ringing in Pockels cells is proposed in this work. It is based on symmetric control of Pockels cell using burst of short positive and negative voltage pulses with the same amplitude instead of a single long pulse for light polarization modulation. Rising and falling edges of pulses of the burst induce symmetrical acoustic waves of the opposite phase and cancel the piezoelectric ringing of the crystal. A new high voltage driver capable of generating positive and negative pulses of tens of nanoseconds of 3 kV magnitude was developed for this purpose. The amplitude of laser beam intensity pulsations caused by the piezoelectric ringing can be reduced up to five times when active suppression method is used for the deuterated potassium dihydrogen phosphate (DKDP) Pockels cell. Such crystals like DKDP, LiNbO3, and LiTaO3 may benefit from the proposed method and find new use in lasers of high repetition rate where piezoelectric ringing is a major limiting factor.

Inhibitory control and its relationship to positivity biases in older adults

Older adults tend to focus on positive information over negative information; a phenomenon commonly referred to as the ‘positivity effect’. Socioemotional Selectivity Theory posits that this effect stems from age-related shifts in goals and relies heavily on the active suppression of negative information. The current study tested the hypothesis that inhibitory control is a key determinant of positivity biases in older adults using anti-saccade and recognition memory tasks. Results indicated a significant correlation between levels of inhibitory control and the positivity effect. These findings highlight the key role played by inhibitory control in determining positivity biases amongst older adults.