Electrosensory Frequency and Intensity Discrimination in the Wave-Type Electric Fish Eigenmannia

Eigenmannia's frequency and intensity discrimination thresholds were determined for a range of seven frequencies (50-1700Hz), centered on a fish's individual discharge frequency, using a conditioned go/no-go paradigm. The threshold criterion was '50% correct choices' (of the rewarded stimulus, S+, over the unrewarded stimulus, S—); this was validated by testing for statistically significantly shorter response latencies for the S+ compared with the S— stimulus. The stimuli consisted of sine wave bursts presented for up to 20 s, repeated at 2 s"1 (rise and fall times of an individual burst, 50 ms; holding time, 250 ms; silence, 150ms). When testing for frequency discrimination, the sine wave bursts alternated in frequency (A/); for intensity discrimination, every other sine wave burst was of increased intensity (A/). The reference stimulus intensity was 30 dB with reference to a fish's individual absolute threshold for a continuous sine wave at that frequency, previously determined using a conditioned go response. Sensory discrimination was best close to a fish's individual discharge frequency. At 30 dB sensation level, fish discriminated frequency differences as small as 0.52 Hz (0.60 and 0.79 Hz in two other individuals) and intensity differences as small as 0.56dB (1 dB in two other fish). At stimulus frequencies different from a fish's discharge frequency, Eigenmannia's frequency discrimination declined at lower frequencies at a rate of up to 1 Hz octave"1, and at higher frequencies at a rate of up to 3 Hz octave"1. For Eigenmannia's intensity discrimination a similar loss was observed: at frequencies lower than a fish's discharge frequency, intensity discrimination thresholds rose at a rate of less than 1 dB octave" *, while the rate was below 2 dB octave"1 for higher frequencies. Compared with other acoustico-lateral senses in lower vertebrates, Eigenmannia's electrosensory frequency and intensity discrimination is unusually high, in the range of that known for audition in the most sensitive higher vertebrates with a cochlea (for example, human). This emphasizes Eigenmannia's specialized 'active' electrosensory system, which detects the presence of a stimulus field as the modulation of a fish's own 'carrier' signal in amplitude and phase (beat analysis), as opposed to 'passive' sensory systems, which must deal with unpredictable signals from the environment as they occur

Polyunsaturated fatty acids in the treatment of attention deficit hyperactivity disorder

Background: Attention deficit/hyperactivity disorder (ADHD) is one of the most common behavioral disorders in children. Insufficient dietary intake of long-chain polyunsaturated fatty acids (LC-PUFAs) has been suggested to have an impact on the development of symptoms of ADHD in children. Individuals with ADHD have been demonstrated to have significantly reduced blood concentrations of PUFAs and, in particular, reduced levels of omega-3 (n-3) PUFAs. These findings suggest that PUFA supplementation may reduce the attention and behavior problems associated with ADHD. Objective: To provide an overview of the efficacy of dietary LC-PUFA supplementation in the treatment of ADHD. Methods: Literature published up until December 2013 on the effects of n-3 PUFA supplementation on ADHD symptoms was obtained using a PubMed search and critically reviewed. Results: Dietary PUFA supplementation appears to have beneficial effects on ADHD symptoms although these effects are small. The clinical relevance of these observations remains to be determined. Conclusion: There is only limited support for the efficacy of PUFA supplementation for the core symptoms of ADHD. Given the small effect sizes regarding PUFA supplementation, it may not be a sufficient therapy for a majority of patients with ADHD

Electrosensory stimulus-intensity thresholds in the weakly electric knifefish Eigenmannia: reduced sensitivity at harmonics of its own organ discharge

The South American knifefish Eigenmannia sp. can detect the electric organ discharges (EODs; 250–600 Hz) of conspecifics when they are superimposed over its own EOD. This study investigates the minimum frequency difference necessary for such signal perception, using the application of sine-wave stimuli. Electrosensory stimulusintensity thresholds were determined for trained fish using stimuli associated with food rewards. These sinewave stimuli were ‘clamped’ to the EOD frequency of the fish. Electrosensory thresholds were also determined for the spontaneous jamming avoidance response (JAR; a change in EOD frequency evoked by a stimulus of sufficiently similar frequency), in this case using unclamped stimuli. Over the wide frequency range investigated (0.3–3.01 times EOD frequency), the lowest stimulus-intensity thresholds of 0.6mVcm21 (peak-to-peak) (0 dB) at a water conductivity of 100mScm21 were found close to (but not exactly at) the EOD fundamental frequency. At exact frequency identity between the EOD and the stimulus, the stimulus-intensity response threshold rose abruptly by more than 10 dB compared with slightly higher or lower stimulus frequencies. A similar ‘needle-like’ threshold increase was found at exactly two and three times the EOD frequency, but neither at harmonic ratios between stimulus and EOD frequency that represent fractions (e.g. at 5:4=1.25, 4:3=1.33, 3:2=1.5 or 5:3=1.67 times EOD frequency) nor at subharmonics such as half or two-thirds of the EOD frequency. The steepest increase of stimulusintensity response threshold was in the range 0.998–1.002 times EOD frequency, corresponding to a threshold change, or electrosensory filter slope, of 5000 dB per octave. For the spontaneous JAR, a similar stimulus-intensity threshold increase was observed when EOD frequency equalled stimulus frequency. Because of the longer rise time for the stimulus amplitude (400 ms rather than 35 ms) the stimulus intensity threshold was higher (up to 32 dB; mean, 20 dB) than in the other experiments (up to 15 dB; mean, 13 dB). A difference in frequency between the EOD and the applied stimulus as small as 1 Hz (that is, 0.2 % of the EOD frequency) was sufficient for good signal perception in Eigenmannia sp. The JAR appears to be useful in avoiding insensitivity at exact integer harmonics of the EOD frequency

Electrosensory phase sensitivity in the weakly electric fish Eigenmannia in the detection of signals similar to its own

The electric organ discharge (EOD) of the South American knifefish Eigenmannia sp. is a permanently present wave signal of usually constant amplitude and frequency (similar to a sine wave). A fish perceives discharges of other fish as a modulation of its own. At frequency identity (∆F = 0 Hz) the phase difference between a fish's own electric discharge and that of another fish affects the superimposed waveform. It was unclear whether or not the electrosensory stimulus- intensity threshold as behaviourally determined depends on the phase difference between a fish's own EOD and a sine-wave stimulus (at ∆F = 0 Hz). Also the strength of the jamming avoidance response (JAR), a discharge frequency shift away from a stimulus that is sufficiently close to the EOD frequency, as a function of phase difference was studied. Sine-wave stimuli were both frequency-clamped and phase-locked to a fish's discharge frequency (∆F = 0Hz). In food-rewarded fish, the electrosensory stimulus-intensity threshold depended significantly on the phase difference between a fish's discharge and the stimulus. Stimulus-intensity thresholds were low (down to 3 µV/cm, peak-to-peak) when the superimposed complex wave changed such that the shift in zero-crossings times relative to the original EOD was large but amplitude change minimal; stimulus-intensity thresholds were high (up to 16.9 µV/cm, peak-to-peak) when the shift in zero-crossings times was small but amplitude change maximal. Similar results were obtained for the non-conditioned JAR: at constant supra-threshold stimulus intensities and ∆F = 0 Hz, the phase difference significantly affected the strength of the JAR, although variability between individuals was higher than that observed in the conditioned experiments

Effects of omega-3 fatty acids and sugar on attention in the spontaneously hypertensive rat

Dietary omega-3 fatty acids and sugar may potentially influence cognition. The effects of reduced omega-3 PUFA and high sugar intakes in rats on attentional functions were investigated. Two groups of rat dams and their offspring were fed either an omega-3 adequate or an omega-3 deficient diet, both with high sucrose/glucose content. A control group was fed an omega-3 adequate diet containing standard levels of sugar. The offspring were tested in a 3-choice-serial-reaction-time task. Compared to controls, statistically significant reductions in attention were found in both omega-3 adequate and omega-3 deficient diet groups, both of which were fed increased amounts of sugar. No significant differences were observed between the latter two groups. These findings demonstrate the detrimental effects of high sugar intake on attention with no exacerbation of these effects by omega-3 PUFA reduction. The interaction between dietary components should be taken into consideration when investigating the effects of nutritional modifications

Alterations of attention and impulsivity in the rat following a transgenerational decrease in dietary omega-3 fatty acids

Polyunsaturated fatty acids (PUFAs), particularly the omega-3 PUFAs, are thought to be involved in neuronal processes, to play a role in neurodevelopmental disorders and to be important for the integrity of central nervous system functioning. The present study investigated the effects of nutritional omega-3 PUFAs on attentional functions and impulsive behavior in Wistar rats. For this purpose, female Wistar rats were fed an omega-3 deficient diet over several generations, and the dams of the seventh generation were randomly assigned to two diet groups and fed an omega-3 deficient or an omega-3 sufficient diet. In addition, a group of previously untreated dams was fed an omega-3 sufficient diet. The male offspring of these three diet groups were tested using an established paradigm for the assessment of attention and impulsive behavior, i.e. a modified version of the five-choice-serial-reaction-time task (5CSRTT). The present data show that the deficiency of omega-3 PUFAs over generations led to substantial changes in attentional processes and impulsive behaviors. The impairments associated with an omega-3 deficiency were partly corrected by treatment with the omega-3 sufficient diet in the last generation of the omega-3 deficient group which showed substantial improvements in attention parameters. While there were no significant effects of dietary modifications on psychomotor activity levels, there was some evidence for changes in impulsive behavior. In conclusion, transgenerational dietary changes in the availability of omega-3 PUFAs led to changes in attentional processes and impulsive behavior in rats, supporting the hypothesis that omega-3 PUFAs play a role in cognitive and behavioral processes. The present findings offer a promising approach in the investigation of the role of omega-3 PUFAs in a variety of cognitive and behavioral domains. Keywords: Omega-3 fatty acid, Polyunsaturated fatty acids, Attention, Impulsivity, Activity, Rat, Neurodevelopmental disorders, Psychiatric disorder