Recent evidence indicates that the nucleus basalis of Meynert, a distinct population of basal forebrain neurons, is a major source of cholinergic innervation of the cerebral cortex. Postmortem studies have previously demonstrated profound reduction in the presynaptic markers for cholinergic neurons in the cortex of patients with Alzheimer's disease and senile dementia of the Alzheimer's type. The results of this study show that neurons of the nucleus basalis of Meynert undergo a profound (greater than 75 percent) and selective degeneration in these patients and provide a pathological substrate of the cholinergic deficiency in their brains. Demonstration of selective degeneration of such neurons represents the first documentation of a loss of a transmitter-specific neuronal population in a major disorder of higher cortical function and, as such, points to a critical subcortical lesion in Alzheimer's patients.

https://science.sciencemag.org/content/sci/215/4537/1237.full.pdf

Alzheimer's disease and senile dementia: loss of neurons in the basal forebrain.

http://aerg.canberra.edu.au/library/sex_general/2002_Devlin_Nagahama_sex_determination_in_fish_review.pdf

Sex determination and sex differentiation in fish: an overview of genetic, physiological, and environmental influences

Recent evidence in natural and semi-natural settings has revealed a variety of left-right perceptual asymmetries among ver- tebrates These include preferential use of the left or right visual hemifield during activities such as searching for food, agonistic re- sponses, or escape from predators in animals as different as fish, amphibians, reptiles, birds, and mammals There are obvious disad- vantages in showing such directional asymmetries because relevant stimuli may be located to the animal's left or right at rando m; there is no a priori association between the meaning of a stimulus (eg, its being a predator or a food item) and its being located to the ani- mal's left or right Moreover, other organisms (eg, predators) could exploit the predictability of behavior that arises from population- level lateral biases It might be argued that lateralization of function enhances cognitive capacity and efficiency of the brain, thus coun- teracting the ecological disadvantages of lateral biases in behavior However, such an increase in brain efficiency could be obtained by each individual being lateralized without any need to align the direction of the asymmetry in the majority of the individuals of the pop- ulation Here we argue that the alignment of the direction of behavioral asymmetries at the population level arises as an "evolutionarily stable strategy" under "social" pressures occurring when individually asymmetrical organisms must coordinate their behavior with the behavior of other asymmetrical organisms of the same or different species

/pdf/survival-with-an-asymmetrical-brain-advantages-and-4nfldlpjsp.pdf

Survival with an asymmetrical brain: Advantages and disadvantages of cerebral lateralization

Publisher Summary Environmental noise can affect acoustic communication through limiting the broadcast area, or active space, of a signal by decreasing signal-to-noise ratios at the position of the receiver. At the same time, noise is ubiquitous in all habitats and is, therefore, likely to disturb animals, as well as humans, under many circumstances. However, both animals and humans have evolved diverse solutions to the background noise problem, and this chapter reviews recent advancements in studies of vocal adaptations to interference by background noise and relate these to fundamental issues in sound perception. The chapter starts with the discussion of sender's side by considering potential evolutionary shaping of species-specific signal characteristics and individual short‐term adjustments of signal features. Subsequently, it focuses on the receivers of signals and reviews their sensory capacities for signal detection, recognition, and discrimination and relates these issues to auditory scene analysis and the ecological concept of signal space. The data from studies on insects, anurans, birds, and mammals, including humans, and to a lesser extent available work on fish and reptiles is also discussed in the chapter.

Acoustic Communication in Noise

Book reviewFishes of the North-eastern Atlantic and the Mediterranean: Volume II. P.J.P. Whitehead, M.-L. Bauchot, J.-C. Hureau, J. Nielsen, E. Tortonese (Editors). UNESCO Press, Paris, 1986, pp. 510–1007, FF 250, Dfl 105.00, ISBN 92-3-002308-6

To categorize variation in disturbance calls of the weakfish Cynoscion regalis and to understand their generation, we recorded sounds produced by differentsized fish, and by similar-sized fish at different temperatures, as well as muscle electromyograms. Single, simultaneous twitches of the bilateral sonic muscles produce a single sound pulse consisting of a two- to threecycle acoustic waveform. Typical disturbance calls at 18 °C consist of trains of 2‐15 pulses with a sound pressure level (SPL) of 74 dB re 20 μPa at 10 cm, a peak frequency of 540 Hz, a repetition rate of 20 Hz and a pulse duration of 3.5 ms. The pulse duration suggests an incredibly short twitch time. Sound pressure level (SPL) and pulse duration increase and dominant frequency decreases in larger fish, whereas SPL, repetition rate and dominant frequency increase and pulse duration decreases with increasing temperature. The dominant frequency is inversely related to pulse duration and appears to be determined by the duration of muscle contraction. We suggest that the lower dominant frequency of larger fish is caused by a longer pulse (=longer muscle twitch) and not by the lower resonant frequency of a larger swimbladder.

/pdf/effects-of-fish-size-and-temperature-on-weakfish-disturbance-31w4p0qkki.pdf

Effects of fish size and temperature on weakfish disturbance calls: implications for the mechanism of sound generation.

The boatwhistle, the mating call of the oyster toadfish Opsanus tau L. undergoes a pronounced seasonal cycle. The fundamental frequency increases to a peak early in the summer and then decreases markedly in the middle of July. The call duration decreases coincident with the fundamental frequency. It is hypothesized that these fluctuations are controlled by hormonal factors although temperature exerts a direct effect on the fundamental frequency. The fundamental frequency of the boatwhistle in early season is higher in southern populations than in northern ones. Part of this increase is attributed to increased temperature of southern waters. Call duration, which is independent of temperature, varies irregularly up and down the coast.

Seasonal and geographical variation of the mating call of the oyster toadfish Opsanus tau L.

Although sound-producing (sonic) muscles attached to fish swimbladders are the fastest known vertebrate muscles, the functional requirement for such extreme speed has never been addressed. We measured movement of the swimbladder caused by sonic muscle stimulation in the oyster toadfish Opsanus tau and related it to major features of the sound waveform. The movement pattern is complex and produces sound inefficiently because the sides and bottom of the bladder move in opposite in and out directions, and both movement and sound decay rapidly. Sound amplitude is related to speed of swimbladder movement, and slow movements do not produce perceptible sound. Peak sound amplitude overlaps fundamental frequencies of the male's mating call because of muscle mechanics and not the natural frequency of the bladder. These findings suggest that rapid muscle speed evolved to generate sound from an inefficient highly damped system.

Movement and sound generation by the toadfish swimbladder.

The teleost gasbladder is believed to aid in fish audition by transferring pressure components of incoming sound to the inner ears. This idea is primarily based on both anatomical observations of the mechanical connection between the gasbladder and the ear, followed by physiological experiments by various researchers. The gasbladder movement has been modeled mathematically as a pulsating bubble. This study is extending the previous work on fish with a physical coupling of the gasbladder and ear by investigating hearing in two species (the blue gourami Trichogaster trichopterus, and the oyster toadfish Opsanus tau) without a mechanical linkage. An otophysan specialist (the goldfish Carassius auratus) with mechanical coupling, is used as the control. Audiograms were obtained with acoustically evoked potentials (e.g., auditory brainstem response) from intact fish and from the same individuals with their gasbladders deflated. In blue gourami and oyster toadfish, removal of gas did not significantly change thresholds, and evoked potentials had similar waveforms. In goldfish thresholds increased by 33–55 dB (frequency dependent) after deflation, and major changes in evoked potentials were observed. These results suggest that the gasbladder may not serve an auditory enhancement function in teleost fishes that lack mechanical coupling between the gasbladder and the inner ear.

Michael L. Fine

Papers

Effects of fish size and temperature on weakfish disturbance calls: implications for the mechanism of sound generation.

Seasonal and geographical variation of the mating call of the oyster toadfish Opsanus tau L.

Movement and sound generation by the toadfish swimbladder.

Variability in the role of the gasbladder in fish audition.

Shallow-water propagation of the toadfish mating call