The National Academy of Sciences founded The National Academies Press (NAP) with the goal of publishing reports of all four national academies. Annually, NAP publishes more than 200 books from the fields of science, engineering and medicine and offers more than 4000 titles in PDF on its website (http://www.nap.edu/) free of charge.

/pdf/the-national-academies-press-3oqc1apmt7.pdf

The National Academies Press

Little is known about the mechanisms that allow the cortex to selectively improve the neural representations of behaviorally important stimuli while ignoring irrelevant stimuli. Diffuse neuromodulatory systems may facilitate cortical plasticity by acting as teachers to mark important stimuli. This study demonstrates that episodic electrical stimulation of the nucleus basalis, paired with an auditory stimulus, results in a massive progressive reorganization of the primary auditory cortex in the adult rat. Receptive field sizes can be narrowed, broadened, or left unaltered depending on specific parameters of the acoustic stimulus paired with nucleus basalis activation. This differential plasticity parallels the receptive field remodeling that results from different types of behavioral training. This result suggests that input characteristics may be able to drive appropriate alterations of receptive fields independently of explicit knowledge of the task. These findings also suggest that the basal forebrain plays an active instructional role in representational plasticity.

https://science.sciencemag.org/content/sci/279/5357/1714.full.pdf

Cortical map reorganization enabled by nucleus basalis activity.

Over the last 2 decades, a large number of neurophysiological and neuroimaging studies of patients with schizophrenia have furnished in vivo evidence for dysconnectivity, ie, abnormal functional integration of brain processes. While the evidence for dysconnectivity in schizophrenia is strong, its etiology, pathophysiological mechanisms, and significance for clinical symptoms are unclear. First, dysconnectivity could result from aberrant wiring of connections during development, from aberrant synaptic plasticity, or from both. Second, it is not clear how schizophrenic symptoms can be understood mechanistically as a consequence of dysconnectivity. Third, if dysconnectivity is the primary pathophysiology, and not just an epiphenomenon, then it should provide a mechanistic explanation for known empirical facts about schizophrenia. This article addresses these 3 issues in the framework of the dysconnection hypothesis. This theory postulates that the core pathology in schizophrenia resides in aberrant N-methyl-D-aspartate receptor (NMDAR)-mediated synaptic plasticity due to abnormal regulation of NMDARs by neuromodulatory transmitters like dopamine, serotonin, or acetylcholine. We argue that this neurobiological mechanism can explain failures of self-monitoring, leading to a mechanistic explanation for first-rank symptoms as pathognomonic features of schizophrenia, and may provide a basis for future diagnostic classifications with physiologically defined patient subgroups. Finally, we test the explanatory power of our theory against a list of empirical facts about schizophrenia.

/pdf/dysconnection-in-schizophrenia-from-abnormal-synaptic-305n6j3pxf.pdf

Dysconnection in Schizophrenia: From Abnormal Synaptic Plasticity to Failures of Self-monitoring

Joris, P. X., C. E. Schreiner, and A. Rees. Neural Processing of Amplitude-Modulated Sounds. Physiol Rev 84: 541–577, 2004; 10.1152/physrev.00029.2003.—Amplitude modulation (AM) is a temporal featu...

https://www.physiology.org/doi/pdf/10.1152/physrev.00029.2003

Neural processing of amplitude-modulated sounds.

The yield of alkenols and cycloalkenols is substantially improved by carrying out the reaction of olefins with formaldehyde in the presence of selected catalysts. In accordance with one embodiment, alk-3-en-1-ols are produced in good yields from isobutylene and formaldehyde in the presence of organic carboxylic acid salts of Group IB metals.

The Organization of the Cochlear Receptor

The auditory sensitivity of the (Sprague-Dawley strain) albino rat was determined by the conditioned suppression technique. The three animals tested were found to have a range of hearing from 250 Hz to 80 kHz at 70 dB (SPL). They were most sensitive to tones of 8 kHz but were almost as sensitive at 38 kHz. In contrast to previously published data, there was no evidence for a highly specialized tuning of the audiogram to tones in the 30-40 kHz region. In general, the audiogram of this strain of albino rat is quite typical of mammals of the same size and, furthermore, closely approximates the mammalian mean in most essential features.

Auditory sensitivity of the albino rat.

1. Responses of neurons in the auditory cortex of the albino rat were examined using microelectrode mapping techniques. Characteristic frequencies were determined for numerous electrode penetrations across the cortical surface in individual animals. A primary auditory area was identified in the posterolateral neocortex that was characterized by short latency responses to tone bursts and tonotopic organization with high frequencies represented rostrally and low frequencies, caudally. Within this area cells with similar characteristic frequencies were aligned in a dorsoventral orientation to form isofrequency contours. 2. Tuning curves obtained from primary auditory cortex were characteristically "V" shaped with Q10's ranging from 0.97 to 28.4. Maximum Q10 values increased monotonically with characteristic frequency (CF). The lowest thresholds at CF closely approximated the behavioral audiogram for the albino rat. Many neurons, however, had CF thresholds well above the behavioral limit. 3. Areas were found dorsal and ventral to the primary auditory cortex in which CF's were clearly discontinuous with the neighboring isofrequency contours. These data suggest the presence of other auditory fields, the detailed characteristics of which have yet to be examined.

/pdf/organization-of-auditory-cortex-in-the-albino-rat-sound-4lvozrhnlp.pdf

Organization of auditory cortex in the albino rat: sound frequency.

Ferrets were tested in a semicircular apparatus to determine the effects of auditory cortical lesions on their ability to localize sounds in space. They were trained to initiate trials while facing...

Contribution of auditory cortex to sound localization by the ferret (Mustela putorius).

The contribution of the dorsal nucleus of the lateral lemniscus (DNLL) to binaural processing was examined by recording single-unit activity in the rat9s inferior colliculus before, during, and after a reversible block of the excitatory activity in DNLL by local injection of kynurenic acid. Recordings were made from the central nucleus of the inferior colliculus with glass micropipettes filled with 3 M sodium acetate. Kynurenic acid (2 mM in Locke9s solution) was injected into the DNLL through one side of a double-barreled glass pipette. The other side of the pipette was filled with Locke9s solution for making control injections and recording neural activity. Pressure injection of 0.7–2.0 microliter of kynurenic acid resulted in the complete cessation of tone- evoked responses in DNLL for periods of 45 min to 1 hr. Tone bursts were delivered separately to the two ears through headphones fitted to the external auditory meatus. Binaural responses in the inferior colliculus were determined by comparing the effects of monaural and binaural stimulation. Attention was focused on neurons that were excited by contralateral stimulation and inhibited by ipsilateral stimulation. Interaural intensity difference (IID) functions were generated by holding contralateral sound pressure constant at 10 dB above threshold while increasing ipsilateral sound pressure level. Prior to kynurenic acid injection, ipsilateral stimulation caused a pronounced suppression of contralaterally evoked single-unit activity. Unilateral injection of kynurenic acid into DNLL reduced the strength of binaural suppression in the contralateral inferior colliculus. In every cell tested, the IID curve in inferior colliculus was shifted following contralateral DNLL injection. The IID curve returned to normal after recovery of neural activity in DNLL. In contrast, no effect was seen in the inferior colliculus ipsilateral to the kynurenic acid injection. The injection of Locke9s solution into DNLL had no effect on IID curves in the inferior colliculus. These data suggest that the DNLL plays a role in binaural processing through an inhibitory influence on responses in the contralateral inferior colliculus.

https://www.jneurosci.org/content/jneuro/12/11/4530.full.pdf

Inhibitory influence of the dorsal nucleus of the lateral lemniscus on binaural responses in the rat's inferior colliculus

Auditory sensitivity of the albino rat was determined using the conditioned suppression of licking technique. The rat was found to have a range of sensitivity to pure tones from 250 Hz to 80 kHz at 70 dB SPL. The point of maximum sensitivity was 8 kHz closely rivaled by higher frequencies up to 38 kHz. Withing this band, tones were detectable at sound pressures from 2–7 dB SPL. For frequencies above 38‐kHz sensitivity rapidly decreased at a rate of about 50 dB per octave. For frequencies below 8‐kHz sensitivity decreased at a rate of about 20 dB per octave. The audiogram supports previous evidence of good hearing around 32–38 kHz [G. Gourevitch and M. H. Hack, J. Comp. Physiol. Psych. 62, 289–291 (1966)], but does not support the idea that the albino rat's hearing is narrowly tuned to this range. Thus, the sensitivity of the albino rat to these frequencies reflects the broadly tuned high frequency hearing which is generally quite good in small mammals, rather than representing a specialized feature of its auditory system. [Supported by grants from NRC and NIH.]

Jack B. Kelly

Papers

Auditory sensitivity of the albino rat.

Organization of auditory cortex in the albino rat: sound frequency.

Contribution of auditory cortex to sound localization by the ferret (Mustela putorius).

Inhibitory influence of the dorsal nucleus of the lateral lemniscus on binaural responses in the rat's inferior colliculus

Auditory sensitivity of the albino rat