Source location encoding in the fish lateral line canal

The position of a hydrodynamic dipole source, as encoded in a linear array of mechano-detecting neuromasts in the fish lateral line canal, was electrophysiologically investigated. Measured excitation patterns along the lateral line were compared to theoretical predictions and were found to be in good agreement. The results demonstrate that information on the position of a vibrating source from a fish is linearly coded in the spatial characteristics of the excitation pattern of pressure gradients distributed along the lateral line canal. Several algorithms are discussed that could potentially be used by a fish to decode lateral line excitation patterns, in order to localise a source and its axis of vibration. Specifically, a wavelet transform of a 1-D excitation pattern is shown to reconstruct a 2-D image of dipole sources located within a distance comparable to the body length of a fish and with a close range spatial accuracy twice the inter-neuromast distance

Rapid responses of the cupula in the lateral line of ruffe (Gymnocephalus cernuus)

Displacements of cupulae in the supraorbital lateral line canal in ruffe (Gymnocephalus cernuus) have been measured using laser interferometry and by applying transient as well as sinusoidal fluid stimuli in the lateral line canal. The cupular displacement in response to impulses of fluid velocity shows damped oscillations at approximately 120 Hz and a relaxation time-constant of 4.4 ms, commensurate with a quality factor of approximately 1.8. These values are in close agreement with the frequency characteristics determined via sinusoidal fluid stimuli, implying that the nonlinearity of cupular dynamics imposed by the gating apparatus of the sensory hair cells is limited in the range of cupular displacements and velocities measured (100-300 nm; 100-300 mu m/s). The measurements also show that cupular displacement instantaneously follows the initial waveform of transient stimuli. The functional significance of the observed cupular dynamics i

Bidirectional information flow in frontoamygdalar circuits in humans: a dynamic causal modeling study of emotional associative learning

Everyday language is replete with descriptions of emotional events that people have experienced and wish to share with others. Such descriptions presumably rely on pairings of affective words and visual information (such as events and pictures) that have been learnt throughout one's development. To study this kind of affective language learning in the brain, we used functional neuroimaging during associative learning of emotional words and pictures. Brain imaging revealed increased activation of both primary emotional areas such as the amygdala and of higher cognitive areas such as the inferior frontal gyrus (IFG) and medial frontal gyrus. The dynamic causal modeling with Bayesian model selection suggested that the IFG first receives the input and that the connections are bidirectional, suggesting that during such emotional picture-word pair learning, the frontal cortex drives the amygdala activation. Specifically, the interaction between the frontal regions and the amygdala was enhanced by active learning involving both negative and positive emotional stimuli as compared with neutral stimuli. This circuit (especially for negative stimuli) converges with emotion regulation circuits. The enhancement in the connectivity might be responsible for the emotional memory effect in this type of learning

Variation of the gene coding for DARPP-32 (PPP1R1B) and brain connectivity during associative emotional learning

Associative emotional learning, which is important for the social emotional functioning of individuals and is often impaired in psychiatric illnesses, is in part mediated by dopamine and glutamate pathways in the brain. The protein DARPP-32 is involved in the regulation of dopaminergic and glutaminergic signaling. Consequently, it has been suggested that the haplotypic variants of the gene PPP1R1B that encodes DARPP-32 are associated with working memory and emotion processing. We hypothesized that PPP1R1B should have a significant influence on the network of brain regions involved in associative emotional learning that are rich in DARPP-32, namely the striatum, prefrontal cortex (comprising the medial frontal gyrus and inferior frontal gyrus (IFG)), amygdala and parahippocampal gyrus (PHG). Dynamic causal models were applied to functional MRI data to investigate how brain connectivity during an associative emotional learning task is affected by different single-nucleotide polymorphisms (SNPs) of PPP1R1B: rs879606, rs907094 and rs3764352. Compared to heterozygotes, homozygotes with GTA alleles displayed increased intrinsic connectivity between the IFG and PHG, as well as increased excitability of the PHG for negative emotional stimuli. We have also elucidated the directionality of these genetic influences. Our data suggest that homozygotes with GTA alleles involve stronger functional connections between brain areas in order to maintain activation of these regions. Homozygotes might engage a greater degree of motivational learning and integration of information to perform the emotional learning task correctly. We conclude that PPP1R1B is associated with the neural network involved in associative emotional learning

Altered resting state connectivity of the default mode network in alexithymia

Alexithymia is a trait characterized by a diminished capacity to describe and distinguish emotions and to fantasize; it is associated with reduced introspection and problems in emotion processing. The default mode network (DMN) is a network of brain areas that is normally active during rest and involved in emotion processing and self-referential mental activity, including introspection. We hypothesized that connectivity of the DMN might be altered in alexithymia. Twenty alexithymic and 18 non-alexithymic healthy volunteers underwent a resting state fMRI scan. Independent component analysis was used to identify the DMN. Differences in connectivity strength were compared between groups. Within the DMN, alexithymic participants showed lower connectivity within areas of the DMN (medial frontal and temporal areas) as compared to non-alexithymic participants. In contrast, connectivity in the high-alexithymic participants was higher for the sensorimotor cortex, occipital areas and right lateral frontal cortex than in the low-alexithymic participants. These results suggest a diminished connectivity within the DMN of alexithymic participants, in brain areas that may also be involved in emotional awareness and self-referential processing. On the other hand, alexithymia was associated with stronger functional connections of the DMN with brain areas involved in sensory input and control of emotion