Introduction to the Amplifier in BI 274 Lab

• Description of the amplifier's role in the recording rig.

  • Responsible for:

  • Taking signal from the recording.

  • Identifying and removing noise (undesirable information not related to neuron activity).

  • Amplifying action potential magnitude in relation to noise.

Purpose of Filtering

• Main focus: Filter out undesirable information from recordings.

• Two types of filters utilized:

  • High Pass Filters: Allow high-frequency information to pass while removing low-frequency information.

  • Low Pass Filters: Allow low-frequency information to pass while removing high-frequency information.

Filter Settings

• Importance of starting positions for filters:

  • High Pass Filter: Set at 0.1 Hz.

  • Low Pass Filter: Set at 20 kHz.

• Rationale:

  • Filtering strips away some action potential information; aim to filter as little as possible.

  • Only need basic identification of neuron activity by LabChart.

Filter Adjustment Guidance

• Users should:

  • Turn dials outwards for lowest frequency filtering.

  • Avoid filtering in the 100 to 300 Hz range for high-pass filters.

  • Also avoid low-pass filters set at 0.3 kHz and 0.1 kHz.

• Explanation using analogy:

  • Filtering is likened to closing curtains on a window; if filters overlap, no signal passes through.

  • Overlapping filters lead to potential loss of signal information.

Sources of Noise: Electromagnetic Interference (EMI)

• Origin of undesirable information:

  • Comes from electromagnetic interference (EMI).

  • Common sources include:

  • Motors

  • Fish tank pumps

  • Light ballasts for microscopes

  • Cellular phones

Shielding Against EMI

• Techniques for minimizing interference:

  • Use of Shielding: Green wire and aluminum tape used to shield signals from electrodes to the amplifier.

  • Faraday Cage: Used to block EMI from entering the recording environment.

Grounding in Amplifier

• Grounding helps reduce EMI impact.

  • Involves a red banana clip connecting the Faraday cage to the amplifier.

Understanding EMI: An Oscillatory Nature

• Description of oscillatory signals.

• Examples of oscillatory phenomena:

  • Seasonal temperature variations (e.g., Maine temperatures between June and January).

  • Diurnal temperature fluctuations (day vs. night temperatures).

  • Seasonal patterns and overall recording importance.

Potential Data Recording Scenarios

• Visualization of raw recording examples:

  • Action potentials represented as peaks in a signal.

  • Presence of both low and high-frequency noise obscuring accurate neuron identification.

  • Must discern actual neuron activity from noise to enable proper recording.

Filtering Process in Action

• Initial steps:

  • Begin with high-pass filter adjustments to remove low-frequency noise.

  • Success in revealing clear action potentials indicative of neuron firings.

• Follow with low-pass filter adjustments to remove high-frequency noise:

  • Goal: Improve clarity of action potentials so LabChart can distinguish them as outputs from the same neuron.

Over-filtering Risks

• Advice against heavy filtering:

  • Avoid adjustments leading to less accuracy in action potential magnitudes.

  • Reducing amplitude too much can misrepresent neuron activity.

• General advice:

  • If adjustments yield no improved outcomes, refrain from further filtering adjustments.

Lab Experience with the Amplifier

• Opportunity for hands-on practice with amplifier settings and functionality in upcoming lab sessions.

  • Emphasis on experiencing and observing the amplifier's effects directly in laboratory settings.