Encoding temporal regularities and information copying in hippocampal circuits

Discriminating, extracting and encoding temporal regularities is a critical requirement in the brain, relevant to sensory-motor processing and learning. However, the cellular mechanisms responsible remain enigmatic; for example, whether such abilities require specific, elaborately organized neural networks or arise from more fundamental, inherent properties of neurons. Here, using multi-electrode array technology, and focusing on interval learning, we demonstrate that sparse reconstituted rat hippocampal neural circuits are intrinsically capable of encoding and storing sub-second-order time intervals for over an hour timescale, represented in changes in the spatial-temporal architecture of firing relationships among populations of neurons. This learning is accompanied by increases in mutual information and transfer entropy, formal measures related to information storage and flow. Moreover, temporal relationships derived from previously trained circuits can act as templates for copying intervals into untrained networks, suggesting the possibility of circuit-to-circuit information transfer. Our findings illustrate that dynamic encoding and stable copying of temporal relationships are fundamental properties of simple in vitro networks, with general significance for understanding elemental principles of information processing, storage and replication

Long-term modification of cortical synapses improves sensory perception

Synapses and receptive fields of the cerebral cortex are plastic. However, changes to specific inputs must be coordinated within neural networks to ensure that excitability and feature selectivity are appropriately configured for perception of the sensory environment. Long-lasting enhancements and decrements to rat primary auditory cortical excitatory synaptic strength were induced by pairing acoustic stimuli with activation of the nucleus basalis neuromodulatory system. Here we report that these synaptic modifications were approximately balanced across individual receptive fields, conserving mean excitation while reducing overall response variability. Decreased response variability should increase detection and recognition of near-threshold or previously imperceptible stimuli, as we found in behaving animals. Thus, modification of cortical inputs leads to wide-scale synaptic changes, which are related to improved sensory perception and enhanced behavioral performance

Learned Value Magnifies Salience-Based Attentional Capture

Visual attention is captured by physically salient stimuli (termed salience-based attentional capture), and by otherwise task-irrelevant stimuli that contain goal-related features (termed contingent attentional capture). Recently, we reported that physically nonsalient stimuli associated with value through reward learning also capture attention involuntarily (Anderson, Laurent, & Yantis, PNAS, 2011). Although it is known that physical salience and goal-relatedness both influence attentional priority, it is unknown whether or how attentional capture by a salient stimulus is modulated by its associated value. Here we show that a physically salient, task-irrelevant distractor previously associated with a large reward slows visual search more than an equally salient distractor previously associated with a smaller reward. This magnification of salience-based attentional capture by learned value extinguishes over several hundred trials. These findings reveal a broad influence of learned value on involuntary attentional capture

The Role of Superior Temporal Cortex in Auditory Timing

Recently, there has been upsurge of interest in the neural mechanisms of time perception. A central question is whether the representation of time is distributed over brain regions as a function of stimulus modality, task and length of the duration used or whether it is centralized in a single specific and supramodal network. The answers seem to be converging on the former, and many areas not primarily considered as temporal processing areas remain to be investigated in the temporal domain. Here we asked whether the superior temporal gyrus, an auditory modality specific area, is involved in processing of auditory timing. Repetitive transcranial magnetic stimulation was applied over left and right superior temporal gyri while participants performed either a temporal or a frequency discrimination task of single tones. A significant decrease in performance accuracy was observed after stimulation of the right superior temporal gyrus, in addition to an increase in response uncertainty as measured by the Just Noticeable Difference. The results are specific to auditory temporal processing and performance on the frequency task was not affected. Our results further support the idea of distributed temporal processing and speak in favor of the existence of modality specific temporal regions in the human brain

Food-associated cues alter forebrain functional connectivity as assessed with immediate early gene and proenkephalin expression

<p>Abstract</p> <p>Background</p> <p>Cues predictive of food availability are powerful modulators of appetite as well as food-seeking and ingestive behaviors. The neurobiological underpinnings of these conditioned responses are not well understood. Monitoring regional immediate early gene expression is a method used to assess alterations in neuronal metabolism resulting from upstream intracellular and extracellular signaling. Furthermore, assessing the expression of multiple immediate early genes offers a window onto the possible sequelae of exposure to food cues, since the function of each gene differs. We used immediate early gene and proenkephalin expression as a means of assessing food cue-elicited regional activation and alterations in functional connectivity within the forebrain.</p> <p>Results</p> <p>Contextual cues associated with palatable food elicited conditioned motor activation and corticosterone release in rats. This motivational state was associated with increased transcription of the activity-regulated genes <it>homer1a</it>, <it>arc</it>, <it>zif268</it>, <it>ngfi-b </it>and c-<it>fos </it>in corticolimbic, thalamic and hypothalamic areas and of proenkephalin within striatal regions. Furthermore, the functional connectivity elicited by food cues, as assessed by an inter-regional multigene-expression correlation method, differed substantially from that elicited by neutral cues. Specifically, food cues increased cortical engagement of the striatum, and within the nucleus accumbens, shifted correlations away from the shell towards the core. Exposure to the food-associated context also induced correlated gene expression between corticostriatal networks and the basolateral amygdala, an area critical for learning and responding to the incentive value of sensory stimuli. This increased corticostriatal-amygdalar functional connectivity was absent in the control group exposed to innocuous cues.</p> <p>Conclusion</p> <p>The results implicate correlated activity between the cortex and the striatum, especially the nucleus accumbens core and the basolateral amygdala, in the generation of a conditioned motivated state that may promote excessive food intake. The upregulation of a number of genes in unique patterns within corticostriatal, thalamic, and hypothalamic networks suggests that food cues are capable of powerfully altering neuronal processing in areas mediating the integration of emotion, cognition, arousal, and the regulation of energy balance. As many of these genes play a role in plasticity, their upregulation within these circuits may also indicate the neuroanatomic and transcriptional correlates of extinction learning.</p

CIRCADIAN RHYTHM VARIATION IN ENDOCRINE BIOMARKER RESPONSES TO HIGH-INTENSITY INTERVAL TRAINING IN COLLEGE AGED MALES

Cyrus Shuler1, Michael G. Bemben1, FACSM, Rebecca Larson1, Michael Pham1, Chinguun Khurelbaatar1, & Debra A. Bemben1, FACSM 1University of Oklahoma, Norman, Oklahoma Circadian rhythms are critical for regulating physiological and behavioral responses during a 24-hour solar cycle. Testosterone (T) and Cortisol (C) are commonly measured as biomarkers of physiological adaptations to exercise, as the T:C ratio is indicative of an anabolic:catabolic state based on their physiological effects on specific tissues. Recently, high-intensity interval training (HIIT) has emerged as an exercise method shown to yield greater improvements in aerobic fitness compared to traditional steady-state aerobic exercise, yet little is known about its effects on hormonal responses. PURPOSE: To examine the effects of time of day on salivary testosterone (sal-T) and salivary cortisol (sal-C) responses to acute bouts of HIIT performed in the morning (AM) and evening (PM), and to examine diurnal variations in the T:C ratio responses to HIIT in college aged men (n=10). METHODS: A 1:2 minute ratio (Work:Recovery) HIIT protocol was employed (W 81% VO2peak, R 40% of VO2peak). Salivary samples were collected prior to (PRE) and immediately post (IP) each exercise session. Salivary samples also were collected for the control day in the AM and PM on the same day to establish baseline hormone concentrations. All salivary samples were assayed using Salimetrics kits at the Salivalab in Carlsbad, California. Testing order was randomized. RESULTS: A significant exercise main effect was observed for sal-T, which increased PRE to IP for both AM and PM sessions (AM PRE: 274.34 ± 91.39 pg/mL; AM IP: 292.16 ± 87.65 pg/mL vs. PM PRE: 233.83 ± 70.50 pg/mL; PM IP: 281.47 ± 93.78 pg/mL, p = 0.041). Sal-C had a significant time of day main effect as the PM session had lower values for both PRE and IP than the AM session (AM PRE: 0.463 ± 0.348 µg/dL; AM IP: 0.491 ± 0.380 µg/dL vs. PM PRE: 0.210 ± 0.110 µg/dL; PM IP: 0.297 ± 0.244 µg/dL, p = 0.029). The T:C ratio also had a significant time of day main effect (AM PRE: 0.083 ± 0.044; AM IP: 0.085 ± 0.043 vs. PM PRE: 0.132 ± 0.056; PM IP: 0.140 ± 0.073, p = 0.013). CONCLUSION: Sal-T responses to acute bouts of HIIT were not affected by time of day; however, sal-C concentrations were lower in the PM session resulting in a more favorable T:C ratio in the afternoon. These findings suggest performing HIIT in the late afternoon may be more beneficial for physiological adaptations