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Abstract
We examined two subjectively distinct memory states that are elicited during recognition
memory in humans and compared them in terms of the gamma oscillations (20-60 Hz) in
the electroencepahalogram (EEG) that they induced. These subjective states, 'recollection'
and 'familiarity' both entail correct recognition but one involves a clear and conscious
recollection of the event including memory for contextual detail whilst the other
involves a sense of familiarity without clear recollection. Here we show that during
a verbal recognition memory test, the subjective experience of 'recollection' induced
higher amplitude gamma oscillations than the subjective experience of 'familiarity'
in the time period 300-500 ms after stimulus presentation. Recollection, but not familiarity,
was also associated with greater functional connectivity in the gamma frequency range
between frontal and parietal sites. Furthermore, the magnitude of the gamma functional
connectivity varied over time and was modulated at 3 Hz. Previous studies in animals
have shown local theta frequency modulation (3-7 Hz) of gamma-oscillations but this
is the first time that a similar effect has been reported in the human EEG.