Lability in the responses of cells in the auditory cortex of squirrel monkeys to species-specific vocalizations

The activity of 28 cells located mainly in the secondary auditory cortex (A II) of awake squirrel-monkeys, was extracellularly recorded for periods of up to 6 h. Seven different species-specific vocalizations, which were repeatedly presented to the monkey, were used as auditory stimuli. Twenty-six cells responded, at least once, to one or more vocalizations; 22 cells revealed some change in their response (pattern or strength) to at least one vocalization ("change in response"). Twenty-one cells exhibited a change in the number and/or type of vocalization to which they responded during the recording period ("change in selectivity"). At some time during the recording period all the responding cells exhibited a "change in response" and/or a "change in selectivity" ("change in responsiveness"). A "change in response" of a cell to a vocalization did not necessarily exclude a "change in selectivity", associated with the same vocalization, later in time and vice-versa. A "change in responsiveness" to one vocalization was not necessarily correlated with "changes in responsiveness" to other vocalizations.