The Cognitive Neuroscience of Music

processes, it is presumably because cognitive processes influence the state of auditory
cortex (e.g. its balance of excitatory and inhibitory activity), which in turn influences how
the cortex responds to the AM oscillation. Thus the aSSR may serve as an ongoing probe
of cortical function, that is, an indirect measure of cognitive processes over time.

       335

Figure 21.6 The aSSR. Panel (A) shows a 400 Hz pure tone with 40 Hz AM. Panel (B) shows the power spec-
trum of the neural response to the tone, recorded from an MEG sensor located over auditory cortex in an adult
human listener. Note the strong peak at 40 Hz (arrow) marking the aSSR and indicating the presence of stimulus-
related cortical activity. Panel (C) shows a power spectrum of the brain signal when the listener hears a 400 Hz
tone without 40 Hz AM. Stimulus-related activity can no longer be distinguished.

0 0.02 0.04 0.06 0.08 0.1 0.12

• 1

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1

Time (s)

Amplitude (V)

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0

0.2

0.4

0.6

Frequency (Hz)

0 5 10 15 20 25 30 35 40 45 50 55

0

0.2

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Signal strength (pT

2 )

Frequency (Hz)

Signal strength (pT

2 )

With AM

Without AM

C

B

A