The magnetite-based receptors in the beak of birds and their role in avian navigation

Iron-rich structures have been described in the beak of homing pigeons, chickens and several species of migratory birds and interpreted as magnetoreceptors. Here, we will briefly review findings associated with these receptors that throw light on their nature, their function and their role in avian navigation. Electrophysiological recordings from the ophthalmic nerve, behavioral studies and a ZENK-study indicate that the trigeminal system, the nerves innervating the beak, mediate information on magnetic changes, with the electrophysiological study suggesting that these are changes in intensity. Behavioral studies support the involvement of magnetite and the trigeminal system in magnetoreception, but clearly show that the inclination compass normally used by birds represents a separate system. However, if this compass is disrupted by certain light conditions, migrating birds show 'fixed direction' responses to the magnetic field, which originate in the receptors in the beak. Together, these findings point out that there are magnetite-based magnetoreceptors located in the upper beak close to the skin. Their natural function appears to be recording magnetic intensity and thus providing one component of the multi-factorial 'navigational map' of birds

Electrophysiological measurement of human auditory function

Contingent negative variations in the presence and amplitudes of brain potentials evoked by sound are considered. Evidence is produced that the evoked brain stem response to auditory stimuli is clearly related to brain events associated with cognitive processing of acoustic signals since their properties depend upon where the listener directs his attention, whether the signal is an expected event or a surprise, and when sound that is listened-for is heard at last

Electrophysiological measurement of human auditory function

Knowledge of the human auditory evoked response is reviewed, including methods of determining this response, the way particular changes in the stimulus are coupled to specific changes in the response, and how the state of mind of the listener will influence the response. Important practical applications of this basic knowledge are discussed. Measurement of the brainstem evoked response, for instance, can state unequivocally how well the peripheral auditory apparatus functions. It might then be developed into a useful hearing test, especially for infants and preverbal or nonverbal children. Clinical applications of measuring the brain waves evoked 100 msec and later after the auditory stimulus are undetermined. These waves are clearly related to brain events associated with cognitive processing of acoustic signals, since their properties depend upon where the listener directs his attention and whether how long he expects the signal

Complementary Roles of Hippocampus and Medial Entorhinal Cortex in Episodic Memory

Spatial mapping and navigation are figured prominently in the extant literature that describes hippocampal function. The medial entorhinal cortex is likewise attracting increasing interest, insofar as evidence accumulates that this area also contributes to spatial information processing. Here, we discuss recent electrophysiological findings that offer an alternate view of hippocampal and medial entorhinal function. These findings suggest complementary contributions of the hippocampus and medial entorhinal cortex in support of episodic memory, wherein hippocampal networks encode sequences of events that compose temporally and spatially extended episodes, whereas medial entorhinal networks disambiguate overlapping episodes by binding sequential events into distinct memories.National Institute of Mental Health Grants (MH51570, MH071702); National Science Foundation (Science of Learning Center grant SBE-0354378

Dynamic BOLD functional connectivity in humans and its electrophysiological correlates

Neural oscillations subserve many human perceptual and cognitive operations. Accordingly, brain functional connectivity is not static in time, but fluctuates dynamically following the synchronization and desynchronization of neural populations. This dynamic functional connectivity has recently been demonstrated in spontaneous fluctuations of the Blood Oxygen Level-Dependent (BOLD) signal, measured with functional Magnetic Resonance Imaging (fMRI). We analyzed temporal fluctuations in BOLD connectivity and their electrophysiological correlates, by means of long (≈50 min) joint electroencephalographic (EEG) and fMRI recordings obtained from two populations: 15 awake subjects and 13 subjects undergoing vigilance transitions. We identified positive and negative correlations between EEG spectral power (extracted from electrodes covering different scalp regions) and fMRI BOLD connectivity in a network of 90 cortical and subcortical regions (with millimeter spatial resolution). In particular, increased alpha (8-12 Hz) and beta (15-30 Hz) power were related to decreased functional connectivity, whereas gamma (30-60 Hz) power correlated positively with BOLD connectivity between specific brain regions. These patterns were altered for subjects undergoing vigilance changes, with slower oscillations being correlated with functional connectivity increases. Dynamic BOLD functional connectivity was reflected in the fluctuations of graph theoretical indices of network structure, with changes in frontal and central alpha power correlating with average path length. Our results strongly suggest that fluctuations of BOLD functional connectivity have a neurophysiological origin. Positive correlations with gamma can be interpreted as facilitating increased BOLD connectivity needed to integrate brain regions for cognitive performance. Negative correlations with alpha suggest a temporary functional weakening of local and long-range connectivity, associated with an idling state

A modeling framework for contact, adhesion and mechano-transduction between excitable deformable cells

Cardiac myocytes are the fundamental cells composing the heart muscle. The propagation of electric signals and chemical quantities through them is responsible for their nonlinear contraction and dilatation. In this study, a theoretical model and a finite element formulation are proposed for the simulation of adhesive contact interactions between myocytes across the so-called gap junctions. A multi-field interface constitutive law is proposed for their description, integrating the adhesive and contact mechanical response with their electrophysiological behavior. From the computational point of view, the initial and boundary value problem is formulated as a structure-structure interaction problem, which leads to a straightforward implementation amenable for parallel computations. Numerical tests are conducted on different couples of myocytes, characterized by different shapes related to their stages of growth, capturing the experimental response. The proposed framework is expected to have impact on the understanding how imperfect mechano-transduction could lead to emergent pathological responses.Comment: 31 pages, 17 figure

Schizotypy: A Multi-Country Study of Psychometrics, Socio-Cultural Influences, Cognitive Processes, and Electrophysiological Markers

Schizotypy represents a latent personality organisation reflecting a putative liability for schizophrenia spectrum disorders. Schizotypic traits include anomalies in cognition (e.g., hallucinations), socio-emotional function (e.g., constricted affect), and behaviour (e.g., odd behaviour and language) that do not meet the clinical threshold for psychotic disorders. This thesis presents a series of studies investigating schizotypal measurement across ethno-cultural settings, examining cognitive antecedents and outcomes of schizotypy, and a schizotypal-continuum exploration into electrophysiological function. Studies 1-3 examined the Schizotypal Personality Questionnaire (SPQ) as a measurement tool for schizotypy. These studies re-evaluated the domain structure of the English SPQ and the German SPQ, and developed and evaluated a Malay translation of the SPQ. Further, through the evaluation and development of these measures, schizotypy was explored within the framework of ethnic and cultural identities. This included evaluations between African Caribbeans in the UK and Trinidad, with White British participants; Malay and Chinese participants in Malaysia, and; central European White participants from Austria and southern Germany, with a similar cultural (migrational) group in the UK. Studies 4a and 4b concerned schizotypy, cognitive processes, and conspiracy ideation. From an initial pilot, associations were established with conspiracy ideation, included as a prima facie outcome of disordered thinking. A follow-up study showed that analytic thinking mediated the relationship between Odd Beliefs or Magical Thinking (but not Ideas of Reference) and belief in conspiracy theories. Study 5 investigated whether a combination of high schizotypal ratings and abnormal electrophysiological function could be established. Second, this study allowed for a unique comparison between culture and ethnicity, within the assessment of electrophysiological function. Finally, this study allowed for an investigation into associations between the domains established in Study 1 (namely, Cognitive-Perceptual, Paranoid, Disorganised, and Negative) and electrophysiological function. Results indicated little evidence of association between the schizotypy and schizophrenia literature; that is, there was no apparent electrophysiological deficits for high schizotypal individuals and no ethno-cultural influence. Further, the results of the regression indicated no support for associations at the higher-order domain level and electrophysiological function. Taken together, these studies informed the schizotypal literature through multiple routes. Indeed, this thesis addressed both the personality (cognitive outcomes) and clinical (electrophysiological) nature of schizotypy with the foundation of a thorough measurement examination

Chronic thoracic hemisection spinal cord injury in adult rats induces a progressive decline in transmission from uninjured fibers to lumbar motoneurons

Although most spinal cord injuries are anatomically incomplete, only limited functional recovery has been observed in people and rats with partial lesions. To address why surviving fibers cannot mediate more complete recovery, we evaluated the physiological and anatomical status of spared fibers after unilateral hemisection (HX) of thoracic spinal cord in adult rats. We made intracellular and extracellular recordings at L5 (below HX) in response to electrical stimulation of contralateral white matter above (T6) and below (L1) HX. Responses from T6 displayed reduced amplitude, increased latency and elevated stimulus threshold in the fibers across from HX, beginning 1-2 weeks after HX. Ultrastructural analysis revealed demyelination of intact axons contralateral to the HX, with a time course similar to the conduction changes. Behavioral studies indicated partial recovery which arrested when conduction deficits began. These findings suggest a chronic pathological state in intact fibers and necessity for prompt treatment to minimize it

The Stiles-Crawford Effect in the Eye of the Blowfly, Calliphora erythrocephala

Stiles-Crawford-like effects (that is, directional sensitivity of the retina) were investigated in the fly’s eye. Intracellular recordings from the visual sense cells were made, and the radiation patterns emerging from the photoreceptors with antidromic light were photographed, and evaluated with a microdensitometer. The measurements from both methods agree well, and can be satisfactorily described by a theoretical model based on waveguide theory. Clear radiation patterns from the first and second order modes were observed at the level of the cornea. As in the vertebrate eye, the photoreceptors are aligned towards the center of the lens, a phenomenon for which a theoretical explanation is proposed.