Subject: Tr: Latency of activation of auditory cortex (fwd)
From: Alexandra Hettergott (firstname.lastname@example.org)
Date: Mon Feb 15 1999 - 08:43:04 EST
From: email@example.com <firstname.lastname@example.org>
To: email@example.com <firstname.lastname@example.org>
Date: Wednesday, January 20, 1999 9:25 PM
Subject: Latency of activation of auditory cortex (fwd)
>---------- Forwarded message ----------
>Date: Wed, 20 Jan 1999 06:33:47 -0800
>From: "David L. Woods" <dlwoods@UCDAVIS.EDU>
>Subject: Latency of activation of auditory cortex
>Your question on the latency of initial excitation of auditory is an
>interesting one from several perspectives. Direct recordings from human
>auditory cortex are probably the gold standard. Celesia was first to obtain
>these, and, if I recall correctly, found initial excitation in the 12-15 ms
>range (1). In later studies(2) , longer latency responses (similar to the
>middle latency AEPs recorded from the scalp) were obtained from lateral
>superior temporal plane locations (distant from primary auditory cortex).
>More recent intracranial studies have been performed by Liegeois-Chauvel in
>France. She found the initial volley arrived at about 13 ms when
>recordings were made in the medial portions of Heschls gyrus(3). Longer
>latency components with higher amplitudes are recorded also recorded at
>medial Heschls gyrus, and larger longer-latency AEPs can also be recorded
>at more lateral locations within the superior temporal plane(4). In
>macaques, Mitch Steinschneider at Albert Einstein has obtained similar
>results -- the time of arrival of the initial thalamo-cortical volley at
>layer 4 of auditory cortex is estimated from intracranial AEPs, current
>source-density analysis, and multiple unit recording is about 8 ms in the
>monkey(5). Larger amplitude AEPs, with longer latencies, are seen at more
>These times of arrival are reasonably consistent with the estimated speed
>of conduction in auditory fibers of the brainstem estimated from brainstem
>auditory evoked potentials (BAEPs). Wave V of the BAEP originates in the
>vicinity of the inferior colliculus, while waves VI and VII (latencies
>about 8 and 10 ms), are often suggested to arise in the medial geniculate
>body and auditory cortex, respectively(6). This is consistent with
>estimates of the conduction velocity in the lateral lemniscus using peak
>latency measures of BAEP components and measures of distances between
>hypothetical generator regions. Incidentally, conduction velocity in humans
>appears to be considerably slower than in sonar-dependent dolphins, where
>huge auditory fibers appear specialized for particularly rapid conduction(7).
>With respect to intensity effects, these are already seen at wave V of the
>BAEP. It shortens by about 20-40 us/dB(8). Some of this shortening is due
>to cochlear displacement -- i.e., in the absence of masking, louder sounds
>excite more basilar portions of the cochlea. Wave V latencies also change,
>as expected, with changes in stimulus frequency (or high frequency hearing
>loss). This reflects in part the time for traveling waves to excite hair
>cells on the basilar membrane. However, there also appear to be alterations
>in the speed of conduction of human auditory fibers, such that a subset of
>high frequency fibers (possibly analogous to magnocellular projections in
>vision) conduct more rapidly -- as reflected in shortened interpeak
>latencies of AEP components(9). These effects (several ms at wave V)
>increase until at N1 latencies (~110 ms), 4.0 kHz tones generate N1s which
>are 15-20 ms shorter in latency than those elicited by loudness-matched 250
>Finally, AEPs suggest that the bulk of auditory processing in conscious
>subjects occurs well after the initial cortical volley. Indeed, the initial
>volley is difficult to detect: its putative reflection on the scalp, wave
>VIII of the BAEP, is invisible in most subjects. Middle latency (10-70 ms)
>AEPs, while detectable, have generally small amplitudes (0.5-2.0 uV),
>whereas the N1 shows 4-10 uV amplitudes, and is relatively even more
>prominent with magnetic recording (N1m). This component occurs at about 10x
>the latency of initial cortical excitation, and has a complex set of
>subcomponents, with tonotopic and non-tonotopic generators(10).
> 1. Celesia, G. G., Broughton, R. J., Rasmussen, T., and Branch, C.
>Auditory evoked responses from the exposed human cortex.
>Electroencephalography & Clinical Neurophysiology, 1968, 24: 458-466.
>2. Celesia, G., and Puletti, F. Auditory input to the human cortex during
>states of drowsiness and surgical anesthesia. Electroencephalography and
>Clinical Neurophysiology, 1971, 31: 603-609.
> 3. Liegeois-Chauvel, C., Musolino, A., and Chauvel, P. Localization of
>the primary auditory area in man. Brain, 1991, 114: 139-51.
> 4. Liegeois-Chauvel, C., Musolino, A., Badier, J. M., Marquis, P., and
>Chauvel, P. Evoked potentials recorded from the auditory cortex in man:
>evaluation and topography of the middle latency components.
>Electroencephalography and Clinical Neurophysiology, 1994, 92: 204-14.
>5. Steinschneider, M., Tenke, C. E., Schroeder, C. E., Javitt, D. C., and
>Vaughan, H. G. Cellular generators of the cortical auditory evoked
>potential initial component. Electroencephalography and Clinical Neuro-
>physiology, 1992, 84: 196-200.
>6. Markand, O. N. Brainstem auditory evoked potentials. Journal Of
>Clinical Neurophysiology, 1994, 11: 319-342.
> 7. Ridgway, S. H., Bullock, T. H., Carder, D. A., Seeley, R. L., and
>Galam- bos, R. Auditory brainstem response in dolphins. Proceedings of
>the National Academy of Sciences, 1981, 78: 1943-47.
> 8. Starr, A. Auditory pathway origins of scalp-derived auditory brainstem
>responses. In G. Morocutti and P. A. Rizzo (Eds.), Evoked Potentials:
>Neurophysiological and Clinical Aspects. Amsterdam: Elsevier, 1985 : 19.
> Woods, D. L., Alain, C., Covarrubias, D., and Zaidel, O. Frequency-
>related differences in the speed of human auditory processing. Hearing
>Research, 1993, 66: 46-52.
> 10. Woods, D. L. The component structure of the N1 wave of the human
>auditory evoked potential. Electroencephalography and Clinical
>Neurophysiology Supplement. Perspectives on Event-Related Potential
>Research, 1994, 44: 102-109.
>David L. Woods, Professor of Neurology, Dept. of Neurology,UC Davis,
>Neurology Service (127), NCSC, 150 Muir Rd., Martinez, CA 94553
>Tel (925) 372-2571, Fax (925) 229-2315 Email:email@example.com
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