Majority Of Neurons Research Articles

Differential Regulation of Primary Afferent Input to Spinal Cord by Muscarinic Receptor Subtypes Delineated Using Knockout Mice

Stimulation of muscarinic acetylcholine receptors (mAChRs) inhibits nociceptive transmission at the spinal level. However, it is unclear how each mAChR subtype regulates excitatory synaptic input from primary afferents. Here we examined excitatory postsynaptic currents (EPSCs) of dorsal horn neurons evoked by dorsal root stimulation in spinal cord slices from wild-type and mAChR subtype knock-out (KO) mice. In wild-type mice, mAChR activation with oxotremorine-M decreased the amplitude of monosynaptic EPSCs in ∼67% of neurons but increased it in ∼10% of neurons. The inhibitory effect of oxotremorine-M was attenuated by the M2/M4 antagonist himbacine in the majority of neurons, and the remaining inhibition was abolished by group II/III metabotropic glutamate receptor (mGluR) antagonists in wild-type mice. In M2/M4 double-KO mice, oxotremorine-M inhibited monosynaptic EPSCs in significantly fewer neurons (∼26%) and increased EPSCs in significantly more neurons (33%) compared with wild-type mice. Blocking group II/III mGluRs eliminated the inhibitory effect of oxotremorine-M in M2/M4 double-KO mice. In M2 single-KO and M4 single-KO mice, himbacine still significantly reduced the inhibitory effect of oxotremorine-M. However, the inhibitory and potentiating effects of oxotremorine-M on EPSCs in M3 single-KO and M1/M3 double-KO mice were similar to those in wild-type mice. In M5 single-KO mice, oxotremorine-M failed to potentiate evoked EPSCs, and its inhibitory effect was abolished by himbacine. These findings indicate that activation of presynaptic M2 and M4 subtypes reduces glutamate release from primary afferents. Activation of the M5 subtype either directly increases primary afferent input or inhibits it through indirectly stimulating group II/III mGluRs.

Odor Processing by Adult-Born Neurons

The adult mammalian brain is continuously supplied with adult-born neurons in the olfactory bulb (OB) and hippocampus, where they are thought to be important for circuit coding and plasticity. However, direct evidence for the actual involvement of these neurons in neural processing is still lacking. We recorded the spiking activity of adult-born periglomerular neurons in the mouse OB invivo using two-photon-targeted patch recordings. We show that odor responsiveness reaches a peak during neuronal development and then recedes at maturity. Sensory enrichment during development enhances the selectivity of adult-born neurons after maturation, without affecting neighboring resident neurons. Thus, in the OB circuit, adult-born neurons functionally integrate into the circuit, where they acquire distinct response profiles in an experience-dependent manner. The constant flow of these sensitive neurons into the circuit provides it with a mechanism of long-term plasticity, wherein new neurons mature to process odor information based on past demands.

Characterization of a novel primary culture system of adult zebrafish brainstem cells

Adult zebrafish (Danio rerio) have a remarkable ability to restore function after an injury to the brain or spinal cord. The molecular and cellular mechanisms underlying this phenomenon are not fully understood. To enable investigation of these mechanisms we have developed an in vitro model system from the adult zebrafish brainstem, which can be maintained under serum-containing and serum-free conditions. While cultures are predominantly neuronal, they also contain glia and stem progenitor cells. Various stages of cellular differentiation are observed among both neuronal and non-neuronal populations. Quantitative morphological results revealed typical cellular growth over a two-week period. We argue that our novel brainstem culture model offers a powerful tool for the studies of axonal growth, neurogenesis, and regeneration in the adult zebrafish central nervous system.

Characterization of human auditory brainstem circuits by calcium-binding protein immunohistochemistry

The cochlear nucleus (CN) and superior olivary complex are auditory brainstem centers with essential roles in encoding temporal features of vocalizations, localization of sound sources and descending modulation of the cochlea. Numerous neuronal populations, across a multitude of laboratory mammals, have been characterized within these brainstem centers based on cell body morphology, dendritic architecture, afferent/efferent connections and neurochemistry. However, scant details are available for these neuronal populations in humans. The objective of this study is to further characterize human auditory hindbrain nuclei and examine the axonal connections between these structures. To this end, we have used immunohistochemistry and morphometric techniques to characterize neuronal populations and axonal projections in the human brainstem. Herein, we provide evidence for calretinin immunoreactive neurons and synaptic boutons in the ventral CN, axons in the trapezoid body, peridendritic boutons in the medial superior olive and calyceal endings in the medial nucleus of the trapezoid body (MNTB). Further, we demonstrate that the majority of neurons in the human MNTB are calbindin and Kv3.1b immunoreactive and that perisomatic profiles in this nucleus are vesicular glutamate transporter and Rab3a positive, suggesting that such profiles are in fact synaptic terminals.

Single-Neuron Mechanisms Underlying Cost-Benefit Analysis in Frontal Cortex

Effective decision-making requires consideration of costs and benefits. Previous studies have implicated orbitofrontal cortex (OFC), dorsolateral prefrontal cortex (DLPFC), and anterior cingulate cortex (ACC) in cost-benefit decision-making. Yet controversy remains about whether different decision costs are encoded by different brain areas, and whether single neurons integrate costs and benefits to derive a subjective value estimate for each choice alternative. To address these issues, we trained four subjects to perform delay- and effort-based cost-benefit decisions and recorded neuronal activity in OFC, ACC, DLPFC, and the cingulate motor area (CMA). Although some neurons, mainly in ACC, did exhibit integrated value signals as if performing cost-benefit computations, they were relatively few in number. Instead, the majority of neurons in all areas encoded the decision type; that is whether the subject was required to perform a delay- or effort-based decision. OFC and DLPFC neurons tended to show the largest changes in firing rate for delay- but not effort-based decisions; whereas, the reverse was true for CMA neurons. Only ACC contained neurons modulated by both effort- and delay-based decisions. These findings challenge the idea that OFC calculates an abstract value signal to guide decision-making. Instead, our results suggest that an important function of single PFC neurons is to categorize sensory stimuli based on the consequences predicted by those stimuli.

Relationship between the Local Structure of Orientation Map and the Strength of Orientation Tuning of Neurons in Monkey V1: A 2-Photon Calcium Imaging Study

A majority of neurons in the monkey primary visual cortex (V1) are tuned to stimulus orientations. Preferred orientations and tuning strengths vary among V1 neurons. The preferred orientation of neurons gradually changes across the cortex with occasional failures of this organization. How V1 neurons are arranged by the strength of orientation tuning and whether neuronal arrangement for tuning strength relates to orientation preference maps remains controversial. In this study, we performed in vivo two-photon calcium imaging in macaque V1 to examine the local spatial organization of orientation tuning at the level of single cells. We recorded fluorescence signals from individual neurons loaded with a calcium-sensitive dye in layer 2 and the uppermost tier of layer 3. The strength of orientation tuning was shared by nearby neurons, and changed across the cortex. The neurons with similar tuning strength were distributed across at least the entire thickness of layer 2. The tuning strength was weaker in regions where neurons exhibited heterogeneous preferred orientations, as compared with regions where neurons shared similar orientation preferences. Nearby direction-selective neurons often shared their preferred directions, although only a few neurons were direction selective in the layers examined. Thus, the orientation tuning strength of V1 neurons is partially predictable from the local structure of orientation map. The weaker orientation tuning we found in regions with heterogeneous orientation preferences suggests that orientation-independent interactions among local populations of V1 neurons play a critical role in determining their orientation tuning.

Short-term episodes of hypoxia induce posthypoxic hyperexcitability and selective death of GABAergic hippocampal neurons

We have previously developed a rat hippocampal neuronal cell model for the registration of the preconditioning effect and posthypoxic hyperexcitability (Turovskaya et al., 2011). Repeated episodes of short-term hypoxia are reported to suppress the amplitude of Ca2+ response to NMDA in majority of neurons, reflecting the effect of preconditioning in the culture. In addition, exposure to hypoxia causes posthypoxic hyperexcitability: this is characterized by the onset of spontaneous synchronous Ca2+ transients in a population of neurons in a neural network during the period of reoxygenation after each hypoxic episode. The nature of this phenomenon is unknown, although it has been observed that there always exists a minority of neurons in which there is no effect of hypoxic preconditioning. In this small population of neurons, the amplitude of Ca2+ response to NMDA is not suppressed, but rather increases after each episode of hypoxia. Here we report the type of these neurons and their role in the generation of posthypoxic hyperexcitability. We compared the effect of short-term hypoxia on the amplitude of the Ca2+ response to NMDA and the Ca2+ transient generation in two populations of neurons — inhibitory GABAergic and excitatory glutamatergic. We have demonstrated that the neurons in which the preconditioning effect was not observed are GABAergic. Moreover at the instant moment of the posthypoxic synchronous Ca2+-transient generation (during reoxygenation) there is a global increase of [Ca2+]i and subsequent apoptosis in some GABAergic neurons. Anti-inflammatory cytokine interleukin-10 prevents the development of posthypoxic hyperexcitability, inhibiting the spontaneous synchronous Ca2+ transients. At the same time, interleukin-10 protects GABAergic neurons from death, by restoring the effect of hypoxic preconditioning in them. Activation of one of the signaling pathways initiated by interleukin-10 appears to be necessary for the development of hypoxic preconditioning in GABAergic neurons. Overall our results indicate that short-term episodes of hypoxia can damage GABAergic neurons and weaken the inhibitory action of GABAergic neurons in a neural network. Activation of PI3K-dependent survival signaling pathways in neurons of this type is a possible strategy to protect these cells against hypoxia.

Developmental Changes in the Expression of TRPV1 Channels in Autonomic Nervous System Neurons

The expression of TRPV1 channels in neurons in sympathetic and afferent ganglia in rat pups of different ages (neonatal, aged 10, 20, 30, 60, and 180 days) were studied immunohistochemically. The results showed that most neurons in the sensory ganglion of the vagus nerve and the spinal ganglia contain TRPV1 channels from birth. During ontogeny, there was a small increase in the proportion of cells containing TRPV1 channels in the spinal ganglia to day 20 of life. The proportion of TRPV1-positive neurons in neurons in the sensory ganglion of the vagus nerve showed no significant developmental change. The sensory ganglion of the vagus nerve all age groups showed higher proportions of TRPV1-immunoreactive neurons than spinal ganglia. In the sympathetic ganglia of neonatal animals, the vast majority of neurons contained TRPV1 channels, after which the proportion of TRPV1-positive neurons decreased sharply, such that there were only occasional neurons containing this type of channel by age 20 days. The final proportion of TRPV1-containing neurons, comparable with that in adults, was reached by the end of the first month of life.

Neuropilin-1 biases dendrite polarization in the retina

The majority of neurons in the nervous system exhibit a polarized morphology, with multiple short dendrites and a single long axon. It is clear that multiple factors govern polarization in developing neurons, and the biased accumulation of intrinsic determinants to one side of the cell, coupled with responses to asymmetrically localized extrinsic factors, appears to be crucial. A number of intrinsic factors have been identified, but surprisingly little is known about the identity of the extrinsic signals. Here, we show in vivo that neuropilin-1 (Nrp1) and its co-receptor plexinA1 (Plxna1) are necessary to bias the extension of the dendrites of retinal ganglion cells to the apical side of the cell, and ectopically expressed class III semaphorins (Sema3s) disrupt this process. Importantly, the requirement for Nrp1 and Plxna1 in dendrite polarization occurs at a developmental time point after the cells have already extended their basally directed axon. Thus, we propose a novel mechanism whereby an extrinsic factor, probably a Sema3, acts through Nrp1 and Plxna1 to promote the asymmetric outgrowth of dendrites independently of axon polarization.

Oscillatory activity in ventrolateral thalamus of patients with Parkinson's disease

Objective To explore the neuronal oscillatory activity in the ventrolateral thalamus (the ventral oral posterior nucleus,Vop/the ventral intermediate nucleus,Vim) in relation to parkinsonian motor signs.Methods 23 patients (M:20,F:3 ; mean age:60.6-± 8.2 years,mean duration of disease:6.6± 3.4 years) with Parkinson's disease (PD) who underwent thalamotomy were studied.Their mean Hoehn & Yahr score was 2.2 ± 0.4,and the unified Parkinson's disease rating scale (UPDRS Ⅲ)during OFFstate was 42.4 ± 12.1.The average L-dopa daily dose was 551.7 ± 219.5 mg.Microelectrode records in Vop/Vim and electromyography (EMG) on contralateral limbs to surgery were simultaneously performed.Single unit analysis,interspike interval (ISI) was used to study neuronal firing rate and pattern.Power spectral analysis was carried out to evaluate neuronal oscillation.Coherence analysis was used to study neuronal activity in relation to limb EMG.Clinical outcome was calculated by (presurgery-postsurgery/presurgery) × 100.Results 190 neurons were identified.Power spectral analysis showed that 60％ (n =114) neurons had oscillatory activity.Of those oscillatory neurons,78％ (n =89) neurons had tremor frequency band (3.0 ～ 7.5 Hz) (TFB).Oscillation showing as same frequency as tremor (P ＜0.05) ; 22％ (n =25) neurons had β frequency band(8 ～ 30 Hz) (βFB) oscillation.Further analysis showed that majority of neurons with TFB oscillation localized in Vim,while majority of neurons with βFB oscillations localized in Vop (t =2.048,P ＜ 0.05).In addition,it was found that the mean firing rate of oscillatory neurons in Vop was significantly lower than those neurons in Vim (24.3 ±9.9 Hz vs 28.5 ± 12.4 Hz,t =1.988,P ＜ 0.05).UPDRS revealed that clinical improvement was 89.7％ for tremor,48.4％ for rigidity and 38.1％ for bradykinesia respectively.Conclusions The data support that neuronal oscillations in the Vop/Vim are involved in parkinsonian symptoms.Neurons with TFB oscillation high densely distributed in the Vim indicate that the Vim is the best target for tremor.Since neurons with βFB oscillation are associated with bradykinesia,and the Vop is presumed pallidal relay nucleus.It is likely that the Vop is effective for parkinsonian bradykinesia/rigidity. Key words: Parkinson' s disease; Ventral thalamic nuclei; Microelectrodes; Neurons ; Oscillation

Mechanisms of cell migration in the adult brain: modelling subventricular neurogenesis

Neurogenesis has been the subject of active research in recent years. Although the majority of neurons form during the embryonic period, neurogenesis continues in restricted regions of the mammalian brain well into adulthood. In rodent brains, neuronal migration is present in the rostral migratory stream (RMS), connecting the subventricular zone to the olfactory bulb (OB). The migration in the RMS is characterised by a lack of dispersion of neuroblasts into the surrounding tissues and a highly directed motion towards the OB. This study uses a simple mathematical model to investigate several theories of migration of neuroblasts through the RMS proposed in the literature, including chemo-attraction, chemorepulsion, general inhibition and the presence of a migration-inducing protein. Apart from the general inhibition model, all the models were able to provide results in good qualitative correspondence with the experimental observations.

The transcription factor Pitx3 is expressed selectively in midbrain dopaminergic neurons susceptible to neurodegenerative stress

The homeodomain transcription factor Pitx3 is critical for the survival of midbrain dopaminergic (mDA) neurons. Pitx3-deficient mice exhibit severe but selective developmental loss of mDA neurons, with accompanying locomotor deficits resembling those seen in Parkinson's disease (PD) models. Here, we identify specific mDA cell subpopulations that are consistently spared in adult Pitx3-hypomorphic (aphakia) mice, demonstrating that Pitx3 is not indiscriminately required by all mDA neurons for their survival. In aphakia mice, virtually all surviving mDA neurons in the substantia nigra (SN) and the majority of neurons in the adjacent ventral tegmental area (VTA) also express calbindin-D28k, a calcium-binding protein previously associated with resistance to injury in PD and in animal models. Cell-mapping studies in wild-type mice revealed that Pitx3 is primarily expressed in the ventral SN, a region particularly susceptible to MPTP and other dopaminergic neurotoxins. Furthermore, Pitx3-expressing SN cells are preferentially lost following MPTP treatment. Finally, SN mDA neurons in Pitx3 hemizygous mice show increased sensitivity when exposed to MPTP. Thus, SN mDA neurons are represented by at least two distinct subpopulations including MPTP-resistant Pitx3-autonomous, calbindin-positive neurons, and calbindin-negative Pitx-3-dependent cells that display elevated vulnerability to toxic injury, and probably correspond to the subpopulation that degenerates in PD. Impairment of Pitx3-dependent pathways therefore increases vulnerability of mDA neurons to toxic injury. Together, these data suggest a novel link between Pitx3 function and the selective pattern of mDA cell loss observed in PD.

Linear Processing of Interaural Level Difference Underlies Spatial Tuning in the Nucleus of the Brachium of the Inferior Colliculus

The spatial location of sounds is an important aspect of auditory perception, but the ways in which space is represented are not fully understood. No space map has been found within the primary auditory pathway. However, a space map has been found in the nucleus of the brachium of the inferior colliculus (BIN), which provides a major auditory projection to the superior colliculus. We measured the spectral processing underlying auditory spatial tuning in the BIN of unanesthetized marmoset monkeys. Because neurons in the BIN respond poorly to tones and are broadly tuned, we used a broadband stimulus with random spectral shapes (RSSs) from which both spatial receptive fields and frequency sensitivity can be derived. Responses to virtual space (VS) stimuli, based on the animal's own ear acoustics, were compared with the predictions of a weight-function model of responses to the RSS stimuli. First-order (linear) weight functions had broad spectral tuning (approximately three octaves) and were excitatory in the contralateral ear, inhibitory in the ipsilateral ear, and biased toward high frequencies. Responses to interaural time differences and spectral cues were relatively weak. In cross-validation tests, the first-order RSS model accurately predicted the measured VS tuning curves in the majority of neurons, but was inaccurate in 25% of neurons. In some cases, second-order weighting functions led to significant improvements. Finally, we found a significant correlation between the degree of binaural weight asymmetry and the best azimuth. Overall, the results suggest that linear processing of interaural level difference underlies spatial tuning in the BIN.

Differential expression of VGLUT1 or VGLUT2 in the trigeminothalamic or trigeminocerebellar projection neurons in the rat

The vesicular glutamate transporters, VGLUT1 and VGLUT2, reportedly display complementary distribution in the rat brain. However, co-expression of them in single neurons has been reported in some brain areas. We previously found co-expression of VGLUT1 and VGLUT2 mRNAs in a number of single neurons in the principal sensory trigeminal nucleus (Vp) of the adult rat; the majority of these neurons sent their axons to the thalamic regions around the posteromedial ventral nucleus (VPM) and the posterior nuclei (Po). It is well known that trigeminothalamic (T-T) projection fibers arise not only from the Vp but also from the spinal trigeminal nucleus (Vsp), and that trigeminocerebellar (T-C) projection fibers take their origins from both of the Vp and Vsp. Thus, in the present study, we examined the expression of VGLUT1 and VGLUT2 in Vp and Vsp neurons that sent their axons to the VPM/Po regions or the cortical regions of the cerebellum. For this purpose, we combined fluorescence in situ hybridization (FISH) histochemistry with retrograde tract-tracing; immunofluorescence histochemistry was also combined with anterograde tract-tracing. The results indicate that glutamatergic Vsp neurons sending their axons to the cerebellar cortical regions mainly express VGLUT1, whereas glutamatergic Vsp neurons sending their axons to the thalamic regions express VGLUT2. The present data, in combination with those of our previous study, indicate that glutamatergic Vp neurons projecting to the cerebellar cortical regions express mainly VGLUT1, whereas the majority of glutamatergic Vp neurons projecting to the thalamus co-express VGLUT1 and VGLUT2.

Inactivation of the Parietal Reach Region Causes Optic Ataxia, Impairing Reaches but Not Saccades

Lesions in human posterior parietal cortex can cause optic ataxia (OA), in which reaches but not saccades to visual objects are impaired, suggesting separate visuomotor pathways for the two effectors. In monkeys, one potentially crucial area for reach control is the parietal reach region (PRR), in which neurons respond preferentially during reach planning as compared to saccade planning. However, direct causal evidence linking the monkey PRR to the deficits observed in OA is missing. We thus inactivated part of the macaque PRR, in the medial wall of the intraparietal sulcus, and produced the hallmarks of OA, misreaching for peripheral targets but unimpaired saccades. Furthermore, reach errors were larger for the targets preferred by the neural population local to the injection site. These results demonstrate that PRR is causally involved in reach-specific visuomotor pathways, and reach goal disruption in PRR can be a neural basis of OA.

Respiratory signaling of locus coeruleus neurons during hypercapnic acidosis in the bullfrog, Lithobates catesbeianus

The locus coeruleus (LC) in the brainstem senses alterations in CO2/pH and influences ventilatory adjustments that restore blood gas values to starting levels in bullfrogs (Lithobates catesbeianus). We hypothesized that neurons of the bullfrog LC are sensitive to changes in CO2/pH and that chemosensitive responses are intrinsic to individual neurons. In addition, we hypothesized putative respiratory control neurons of the bullfrog LC would be stimulated by hypercapnic acidosis within physiological ranges of PCO2/pH. 84% of LC neurons depolarized and increased firing rates during exposure to hypercapnic acidosis (HA). A pH dose response curve shows LC neurons from bullfrogs increase firing rates during physiologically relevant CO2/pH changes. With chemical synapses blocked, half of chemosensitive neurons lost sensitivity to HA; however, gap junction blockade did not alter chemosensitive responses. Intrinsically chemosensitive neurons increased input resistance during HA. These data demonstrate that majority of neurons within the bullfrog LC elicit robust firing responses during physiological ΔCO2/pH, likely enabling adjustment of acid–base balance through breathing.

Anterior-Posterior Direction Opponency in the Superficial Mouse Lateral Geniculate Nucleus

We show functional-anatomical organization of motion direction in mouse dorsal lateral geniculate nucleus (dLGN) using two-photon calcium imaging of dense populations in thalamus. Surprisingly, thesuperficial 75μm region contains anterior and posterior direction-selective neurons (DSLGNs) intermingled with nondirection-selective neurons, while upward- and downward-selective neurons are nearlyabsent. Unexpectedly, the remaining neurons encode both anterior and posterior directions, forming horizontal motion-axis selectivity. A model of random wiring consistent with these results makes quantitative predictions about the connectivity of direction-selective retinal ganglion cell (DSRGC) inputs to the superficial dLGN. DSLGNs are more sharply tuned than DSRGCs. These results suggest that dLGN maintains and sharpens retinal direction selectivity and integrates opposing DSRGC subtypes in a functional-anatomical region, perhaps forming a feature representation for horizontal-axis motion, contrary to dLGN being a simple relay. Furthermore, they support recent conjecture that cortical direction and orientation selectivity emerge in part from a previously undescribed motion-selective retinogeniculate pathway.

Gating of Fear in Prelimbic Cortex by Hippocampal and Amygdala Inputs

The prefrontal cortex (PFC) regulates emotional responses, but it is unclear how PFC integrates diverse inputs to select the appropriate response. We therefore evaluated the contribution of basolateral amygdala (BLA) and ventral hippocampus (vHPC) inputs to fear signaling in the prelimbic (PL) cortex, a PFC region critical for the expression of conditioned fear. In conditioned rats trained to press for food, BLA inactivation decreased the activity of projection cells in PL, and reduced PL conditioned tone responses. In contrast, vHPC inactivation decreased activity of interneurons in PL and increased PL conditioned tone responses. Consistent with hippocampal gating of fear after extinction, vHPC inactivation increased fear and PL pyramidal activity in extinguished, but not in conditioned, rats. These results suggest a prefrontal circuit whereby hippocampus gates amygdala-based fear. Thus, deficient hippocampal inhibition of PFC may underlie emotional disorders, especially in light of reduced hippocampal volume observed in depression and PTSD.

Development of the Islands of Calleja

The Islands of Calleja are aggregations of granule cells located in the basal forebrain of most vertebrate species. These cellular aggregations are typically classified as consisting of a single island, the insula magna located adjacent to the nucleus accumbens, and numerous small islands scattered among the dorsal aspect of the olfactory tubercle. While these structures have been widely described in adult, comparatively little is known about their development. Islands are first identifiable at P2–P4 with formation of the Insula Magna and several small aggregations in the caudolateral aspect of the basal forebrain. The Insula Magna fully forms at approximately P4, with continued formation of the small islands through P10 in a caudal to rostral gradient. Historically, there has been controversy as to whether neurons in the islands are GABAergic, due to limitations in resolving immunolabeling for GABA in the densely packed islands. We investigated the neurochemical identity of island cells by exploiting transgenic reporter mice expressing green fluorescent protein under the control of the GAD65 promoter. This demonstrated that the majority of neurons in the Islands of Calleja are GABAergic, primarily utilizing GAD65. Interestingly, several calcium binding protein expressing interneuron classes are present in the postnatal islands, but disappear with maturation. These findings show that the SVZ derived progenitors that migrate to the Islands of Calleja form different lineages to those destined for the olfactory bulbs, despite generation of both populations at the same age/location in the SVZ.

Auditory abstraction from spectro-temporal features to coding auditory entities

The auditory system extracts behaviorally relevant information from acoustic stimuli. The average activity in auditory cortex is known to be sensitive to spectro-temporal patterns in sounds. However, it is not known whether the auditory cortex also processes more abstract features of sounds, which may be more behaviorally relevant than spectro-temporal patterns. Using recordings from three stations of the auditory pathway, the inferior colliculus (IC), the ventral division of the medial geniculate body (MGB) of the thalamus, and the primary auditory cortex (A1) of the cat in response to natural sounds, we compared the amount of information that spikes contained about two aspects of the stimuli: spectro-temporal patterns, and abstract entities present in the same stimuli such as a bird chirp, its echoes, and the ambient noise. IC spikes conveyed on average approximately the same amount of information about spectro-temporal patterns as they conveyed about abstract auditory entities, but A1 and the MGB neurons conveyed on average three times more information about abstract auditory entities than about spectro-temporal patterns. Thus, the majority of neurons in auditory thalamus and cortex coded well the presence of abstract entities in the sounds without containing much information about their spectro-temporal structure, suggesting that they are sensitive to abstract features in these sounds.