Biomedical subjects

L M Aitkin

Publications and source records attributed to L M Aitkin.

At least 55 records · Page 3Linked to original sources

PubMed1978

External nucleus of inferior colliculus: auditory and spinal somatosensory afferents and their interactions.

1. The discharges of 129 units were studied in the external nucleus of the inferior colliculus of 11 anesthetised and paralyzed cats. This region is known to receive fibers from auditory nuclei and the dorsal column nuclei. 2. Stimuli used were pure tone bursts, monaural or binaural, tactile stimulation of the body surface, and electrical stimulation of the dorsal columns (DC) at a low cervical level and of the contralateral and ipsilateral tibial nerves. 3. Forty-six percent of units were only influenced by one type of stimulation (26% auditory, 20% DC). Of the remaining bimodally influenced units, the majority was excited by pure tone stimuli and inhibited by DC stimulation. 4. A small proportion of the total population (18%) was excited by both DC and auditory input, and units sensitive to both tones and tactile stimulation of the skin were rare (4%). 5. Auditory tuning curves were generally very broad compared with those of units in the central nucleus of the inferior colliculus. Similarly, somatic receptive fields were large and usually extended over a whole limb. 6. The majority of tone-responsive units were influenced binaurally (70%); most somatic receptive fields were located on the contralateral fore- or hindlimb (16/18). 7. The results indicate that both auditory and somatosensory information is contained in the discharges of units in the external nucleus of the inferior colliculus. 8. Speculations are made about the role of this nucleus in descending auditory input to the spinal cord and in the comparison of auditory and cutaneous information during sound-evoked coordinated body movements.

Acoustic Stimulation↗

PubMed1975

Responses of single units in cerebellar vermis of the cat to monaural and binaural stimuli.

The responses of 146 cerebellar neurons to tone stimuli were studied in 29 cats anesthetized with chloralose-urethan and in 7 decerebrate preparations. Units were classified as onset or sustained firing. Onset spikes occurred on stimulation of either ear and showed binaural facilitation, while sustained discharges were frequently only excited by monaural stimulation. The latent periods of sustained discharges appeared to be shorter than those of onset responses, and sustained discharges were also more sharply tuned than the onset units. Evidence was presented suggesting that onset responses reflected input from the inferior colliculus and sustained responses, the cochlear nucleus. The sterotyped facilitatory behavior of onset units suggested that a maximal discharge might occur if sounds were of equal intensity at each ear; 26 neurons were examined with variable interaural time or intensity differences and 10 of these exhibited maximal firing when the interaural time and intensity difference was zero--i.e., if the sound was located directly in front of the head.

Acoustic Stimulation↗

PubMed1975

Inferior colliculus. I. Comparison of response properties of neurons in central, pericentral, and external nuclei of adult cat.

The responses of 150 units in the central (ICC), pericentral (ICP), and external nuclei (ICX) of the inferior colliculus of the anesthetized cat were studied in relation to their tuning characteristics and binaural responses to tonal stimuli. Units in ICC were characterized by sharp tuning and binaural responses, while those in ICP and ICX were frequently very broadly tuned with a poorly defined best frequency. Nonetheless, in the latter nuclei a tendency existed for tonotopic organization to occur with high frequencies located externally and low frequencies at the margins of the central nucleus. Tuning measurements were hampered by the common occurrence of habituation in the discharges of single units in ICP and, to a lesser extend, ICX. The majority of units in ICP could be differentiated from those in ICX by their monaural input. Speculations were advanced linking anatomical cell types to physiological responses in the three nuclei and into the possible functional significance of the different behavior of units to tonal stimuli.

Animals↗

PubMed1975

Inferior colliculus. II. Development of tuning characteristics and tonotopic organization in central nucleus of the neonatal cat.

Tuning curves were measured for 65 units in the inferior colliculus of seven anesthetized kittens aged from 6 to 28 days. At 2 days of age the inferior colliculus was divisible into central, pericentral, and external nuclei. Evidence was found for broader tuning curves to occur in the pericentral nucleus compared with the central nucleus, as has been observed in the adult. The middle ear was filled with serous fluid to 6 days, while the external auditory meatus remained collapsed until 10 days. Central nucleus tuning curves in kittens were relatively flat with high thresholds. Best-frequency thresholds diminished from a mean of near 100 dB SPL at 6-11 days to near 50 dB in the adult. The marked drop in thresholds between days 22 and 21 led to the adoption of the sharp form of tuning curve common for adults. Tonotopic organization of the central nucleus was clear at day 11. Speculations were advanced about the dependence of central auditory maturations on cochlear development, axon myelination in the auditory pathway, and changes in synaptic density as a function of age.

Animals↗

PubMed1974