Responses to the purr call in three areas of the guinea pig auditory cortex.

Single electrodes were used to record from anaesthetized animals stimulated with a closed sound system. Neural responses to the purr call were very different in the dorsocaudal core field and in two long-latency belt areas, the ventrorostral belt and the dorsocaudal belt. Responses in the dorsocaudal core field were accurately timed to the start of the nine rhythmic pulses within the purr while the ventrorostral belt responses were more sustained and less temporally precise and most dorsocaudal belt units did not respond.

Encoding of learned importance of sound by magnitude of representational area in primary auditory cortex.

We hypothesized that learning-induced representational expansion in the primary auditory cortex (AI) directly encodes the degree of behavioral importance of a sound. Rats trained on an operant auditory conditioning task were variably motivated to the conditioned stimulus (CS) through different levels of water deprivation. Mean performance values correlated with deprivation level, validating them as a measure of the overall control and, therefore, behavioral importance of the CS.

Characterisation of multiple physiological fields within the anatomical core of rat auditory cortex.

The organisation and response properties of the rat auditory cortex were investigated with single and multi-unit electrophysiological recording. Two tonotopically organised 'core' fields, i.e.

Spectrotemporal receptive field properties of single units in the primary, dorsocaudal and ventrorostral auditory cortex of the guinea pig.

We report the spectrotemporal response properties of single units in the primary (A1) and dorsocaudal (DC) fields, and the ventrorostral belt of the urethane-anaesthetised guinea pig auditory cortex. Using reverse correlation analysis, spectrotemporal receptive fields (STRFs) were constructed and subsequently classified according to a novel qualitative scheme that was based on the duration and bandwidth of excitatory and inhibitory regions within the STRF. The STRFs of units in both A1 and DC showed either broad-band (> or = 1 octave) or narrow-band (< 1 octave) excitatory and inhibitory regions occurring either alone or together.

Interconnections of auditory areas in the guinea pig neocortex.

By studying the efferent projections of five auditory areas in the guinea pig cortex, we sought evidence that the larger fields can be divided into subareas based on unique patterns of cortical connections. Small extracellular injections of biocytin were made in combination with evoked potential mapping or single-unit analysis and histochemical determination of cortical landmarks. The two core fields, primary (AI) and dorsocaudal (DC), are partially surrounded by six adjacent belt areas, leaving two gaps: one at the rostral edge of AI and the other at the dorsal edge.