Lecture 3 - Single Unit Recording & Audition (Cognitive Neuroscience, UU)

Single unit recording: record action potentials from individual neurons

• Differences with EEG: AP are much more localized and the AP are the output activity from the neuron

Two types of recording:

• Intracellular recording: the electrode is placed within the actual cell
  • + you can see what an individual cell is doing, - it is challenging
• Extracellular recording: electrode in outer cellular space

How do we study unit activity with respect to a stimulus or cognitive task?

1. Record raw electrical field inside brain
2. Signal conditioning (filtering)
3. ‘Spike sorting’
4. Analyze ‘event’ epochs (stimulus or behavior) create raster plots for analyses per unit

Rasterplot + peristimulus time histogram (PSTH):

Multielectrode recordings: many recordings. Includes high density multi-electrode recording

• Purpose: more data (reduction of # of experimental animals) and better data (because parallel recording of multiple units tell you something about how they function in a system). So you can study local circuits.

Local waves are related: they travel across the cortex. Many start frontally and end up in the medial temporal lobe.

Sound is compressed air. Single harmonic sounds = pure tone, single frequency, sinusoidal.

Complex harmonic sounds:

Outer ear: amplifies sound, particularly at the frequency range between 2-5 kHz, a range that is important for speech perception. Helps in front-back localization.

Middle ear: transduces air sound waves in outer ear to fluid sound waves in inner ear.

Inner ear: Transduction of sound into neural activity

Basilar membrane: vibrates, properties change along the length so the resonance differs. So every spot will prefer to vibrate at a specific frequency.

Cochleogram: excitation of basilar membrane by sound as a function of time and place.

There are ion channels in the hair tips  are sensitive to movement. When the hair moves the gate will open and will depolarize and a neurotransmitter will be released.

• Cochlear nuclei share auditory information
• Superior olivary complex gets information about two sides so that we can localize sounds
• Nucleus of lateral lemniscus: only gets information from 1 side (contralateral)
• Inferior colliculus receives input from previous 2 stations. Localizes sounds.
• Information is routed to the thalamus. Relays sensory information from periphery to cortex.

Tonotopic organization is present throughout primary auditory pathway.

Speech is lateralized.

The main subjective quality of sounds are:

• Loudness: amplitude
• Pitch: how high a sound is and its perceptual quality.
• Timbre: sound color

Auditory system does not simply report physical characteristics of sounds, but relation between physics and percept is complex.

Harmonic series are very typical of many ‘natural’ sounds, such as voices, rattles etc.

We use two separate mechanisms that determine two different physical phenomena to localize sounds:

1. Interaural time differences (if sound comes from the left, it reaches the left ear sooner than the right ear). This is for low frequencies.
2. Interaural intensity differences. This is for high frequencies.

Summary auditory perception:

• Transduction of sound into action potentials
• Basilar membrane resonance characteristics creates a filter bank for time-frequency analysis, forming the base of the tonotopic map found in the auditory processing pathway
• Relationship between acoustic features and auditory qualities (pitch, timbre, loudness) is complex
• Two separate neural circuits underlie perception of sound localization. 

Questions? Let me know in the contribution section!

Follow me for more summaries / lecture notes!