Biomedical subjects

Ben H Bonham

Publications and source records attributed to Ben H Bonham.

3 recordsLinked to original sources

PubMed2005

Functional organization and hemispheric comparison of primary auditory cortex in the common marmoset (Callithrix jacchus).

Hemispheric fine-grain maps of primary auditory cortex (AI) were derived from microelectrode penetrations in the temporal gyrus of the common marmoset (Callithrix jacchus) to 1) compare the functional organization of AI in the marmoset with other mammalian species and 2) compare the right and left AI maps in individual monkeys. Frequency receptive fields (FRFs) were recorded with pure tones. Five FRF parameters were analyzed: characteristic frequency, threshold, sharpness of tuning 10 dB and 40 dB above threshold, and minimum response latency. The present study confirms that the functional organization of AI is characterized by a robust tonotopic frequency gradient overlaid with spatially clustered distributions of other FRF parameters. Globally, this functional organization of AI in the common marmoset is similar to that in other mammalian species. With respect to within-subject hemispheric comparisons of the five FRF parameters, a coherent pattern of asymmetry is not evident in marmoset AI. The overall results indicate that the basic functional organization between hemispheres is similar but not identical.

Acoustic Stimulation↗

PubMed2005

Functional organization of squirrel monkey primary auditory cortex: responses to frequency-modulation sweeps.

The squirrel monkey twitter call is an exemplar of a broad class of species-specific vocalizations that contain naturally voiced frequency-modulated (FM) sweeps. To investigate how this prominent communication call element is represented in primary auditory cortex (AI), neuronal receptive field properties to pure-tone and synthetic, logarithmically spaced FM-sweep stimuli in 3 barbiturate-anesthetized squirrel monkeys are studied. Responses to pure tones are assessed by using standard measures of frequency response areas, whereas responses to FM sweeps are classified according to direction selectivity, best speed, and speed tuning preferences. Most neuronal clusters respond to FM sweeps in both directions and over a range of FM speeds. Center frequencies calculated from the average of high and low trigger frequency edges of FM response profiles are highly correlated with pure-tone characteristic frequencies (CFs). However, bandwidth estimates are only weakly correlated with their pure-tone counterparts. CF and direction selectivity are negatively correlated. Best speed maps reveal idiosyncratically positioned spatial aggregation of similar values. In contrast, direction selectivity maps show unambiguous spatial organization. Neuronal clusters selective for upward-directed FM sweeps are located in ventral-caudal AI, where CFs range from 0.5 to 1 kHz. Combinations of pure-tone and FM response parameters form 2 significant factors to account for response variations. These results are interpreted in the context of earlier FM investigations and neuronal encoding of dynamic sounds.

Acoustic Stimulation↗

PubMed2003

Spatial organization of frequency response areas and rate/level functions in the developing AI.

The current study was conducted to extend our understanding of changes in spatial organization and response properties of cortical neurons in the developing mammalian forebrain. Extracellular multiunit responses to tones were recorded from a dense array of penetrations covering entire isofrequency contours in the primary auditory cortex (AI) of pentobarbital anesthetized kittens. Ages ranged from postnatal day 14 (P14), shortly after acquisition of normal auditory response thresholds, through postnatal day 111 (P111), when the kittens were largely mature. Spatial organization of the AI was tonotopically ordered by P14. The tonotopic gradient decreased with chronological maturation. At P14 the gradient was about 3.5 kHz/mm. By P111 it had declined to about 2.5 kHz/mm, so that the cortical region encompassing a fixed 3- to 15-kHz frequency range enlarged along its posterior-anterior dimension. Response properties of developing AI neurons changed in both frequency selectivity and intensity selectivity. The mean frequency tuning bandwidth increased with age. Initially, tuning bandwidths were narrow throughout the entire AI. With progressive maturation, broader bandwidths were observed in areas dorsal and ventral to a central region in which neurons remained narrowly tuned. The resulting spatial organization of tuning bandwidth was similar to that reported in adult cats. The majority of recording sites manifested nonmonotonic rate/level functions at all ages. However, the proportion of sites with monotonic rate/level functions increased with age. No spatial organization of rate/level functions (monotonic and nonmonotonic) was observed through P111. The relatively late development of bandwidth tuning in the AI compared with the early presence of tonotopic organization suggests that different developmental processes are responsible for structuring these two dimensions of acoustic selectivity.

Acoustic Stimulation↗