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Acta Neurobiologiae Experimentalis 2004This is a review of our work on multiple microelectrode recordings from the visual cortex of monkeys and subdural recordings from humans--related to the potential... (Review)
Review
This is a review of our work on multiple microelectrode recordings from the visual cortex of monkeys and subdural recordings from humans--related to the potential underlying neural mechanisms. The former hypothesis of object representation by synchronization in visual cortex (or more generally: of flexible associative processing) has been supported by our recent experiments in monkeys. They demonstrated local synchrony among rhythmic or stochastic gamma-activities (30-90 Hz) and perceptual modulation, according to the rules of figure-ground segregation. However, gamma-synchrony in primary visual cortex is restricted to few millimeters, challenging the synchronization hypothesis for larger cortical object representations. We found that the spatial restriction is due to gamma-waves, traveling in random directions across the object representations. It will be argued that phase continuity of these waves can support the coding of object continuity. Based on models with spiking neurons, potentially underlying neural mechanisms are proposed: (i) Fast inhibitory feedback loops can generate locally synchronized gamma-activities; (ii) Hebbian learning of lateral and feed forward connections with distance-dependent delays can explain the stabilization of cortical retinotopy, the limited size of synchronization, the occurrence of gamma-waves, and the larger receptive fields at successive levels; (iii) slow inhibitory feedback can support figure-ground segregation; (iv) temporal dispersion in far projections destroys coherence of fast signals but preserves slow amplitude modulations. In conclusion, it is proposed that the hypothesis of flexible associative processing by gamma-synchronization, including coherent representations of visual objects, has to be extended to more general forms of signal coupling.
Topics: Animals; Association Learning; Cortical Synchronization; Electrophysiology; Haplorhini; Microelectrodes; Visual Cortex; Visual Perception
PubMed: 15366256
DOI: 10.55782/ane-2004-1509 -
Neuron Dec 2012Some have claimed that the medial prefrontal cortex (mPFC) mediates decision making. Others suggest mPFC is selectively involved in the retrieval of remote long-term... (Review)
Review
Some have claimed that the medial prefrontal cortex (mPFC) mediates decision making. Others suggest mPFC is selectively involved in the retrieval of remote long-term memory. Yet others suggests mPFC supports memory and consolidation on time scales ranging from seconds to days. How can all these roles be reconciled? We propose that the function of the mPFC is to learn associations between context, locations, events, and corresponding adaptive responses, particularly emotional responses. Thus, the ubiquitous involvement of mPFC in both memory and decision making may be due to the fact that almost all such tasks entail the ability to recall the best action or emotional response to specific events in a particular place and time. An interaction between multiple memory systems may explain the changing importance of mPFC to different types of memories over time. In particular, mPFC likely relies on the hippocampus to support rapid learning and memory consolidation.
Topics: Association Learning; Decision Making; Hippocampus; Humans; Memory; Neural Pathways; Prefrontal Cortex
PubMed: 23259943
DOI: 10.1016/j.neuron.2012.12.002 -
The Journal of Neuroscience : the... Nov 2013The mesocorticolimbic system, consisting, at its core, of the ventral tegmental area, the nucleus accumbens, and medial prefrontal cortex, has historically been... (Review)
Review
The mesocorticolimbic system, consisting, at its core, of the ventral tegmental area, the nucleus accumbens, and medial prefrontal cortex, has historically been investigated primarily for its role in positively motivated behaviors and reinforcement learning, and its dysfunction in addiction, schizophrenia, depression, and other mood disorders. Recently, researchers have undertaken a more comprehensive analysis of this system, including its role in not only reward but also punishment, as well as in both positive and negative reinforcement. This focus has been facilitated by new anatomical, physiological, and behavioral approaches to delineate functional circuits underlying behaviors and to determine how this system flexibly encodes and responds to positive and negative states and events, beyond simple associative learning. This review is a summary of topics covered in a mini-symposium at the 2013 Society for Neuroscience annual meeting.
Topics: Animals; Association Learning; Dopamine; Dopaminergic Neurons; Nerve Net; Nucleus Accumbens; Prefrontal Cortex; Reward; Ventral Tegmental Area
PubMed: 24198347
DOI: 10.1523/JNEUROSCI.3250-13.2013 -
Acta Neurobiologiae Experimentalis 2016Fear-conditioning is one of the most widely used paradigms in attempts to unravel the processes and mechanisms underlying learning and plasticity. In most of the... (Review)
Review
Fear-conditioning is one of the most widely used paradigms in attempts to unravel the processes and mechanisms underlying learning and plasticity. In most of the Pavlovian conditioning paradigms auditory stimulus is used as a conditioned stimulus (CS), but conditioning can be accomplished also to tactile CS. The whisker-to-barrel tactile system in mice offers convenient way to investigate the brain pathways and mechanisms of learning, and plasticity of the brain cortex. To support a claim that an animal learns during conditioning session and that the plastic changes are associative in nature, objective measures of behavior are necessary. Multiple types of conditioned responses can develop, depending on the training situation, CS and unconditioned stimulus (UCS) characteristics. These include physiological responses, such as salivation, heart rate, galvanic skin reaction, and also behavioral responses, such as startle reflex potentiation or suppression of the ongoing behavior. When studying learning with the whisker system in behaving mice, stimulation of individual whiskers in a well-controlled manner may require animal restrain with a disadvantage of only limited behavioral responses observed. Stimulation of whiskers in the neck-restraining apparatus evokes head movements. When whiskers stimulation (CS) is paired with an aversive UCS during conditioning, the head movements decrease in the course of the training. This reaction, called minifreezing, resembles freezing response, frequently used behavioral measure, however applicable only in freely moving animals. This article will review experimental evidences confirming that minifreezing is a relevant index of association formation between the neutral CS and the and the aversive UCS.
Topics: Animals; Association Learning; Conditioning, Classical; Fear; Mice; Vibrissae
PubMed: 27373946
DOI: 10.21307/ane-2017-008 -
The Journal of Neuroscience : the... Mar 2020Memories for past experiences can range from vague recognition to full-blown recall of associated details. Electroencephalography has shown that recall signals unfold a...
Memories for past experiences can range from vague recognition to full-blown recall of associated details. Electroencephalography has shown that recall signals unfold a few hundred milliseconds after simple recognition, but has only provided limited insights into the underlying brain networks. Functional magnetic resonance imaging (fMRI) has revealed a "core recollection network" (CRN) centered on posterior parietal and medial temporal lobe regions, but the temporal dynamics of these regions during retrieval remain largely unknown. Here we used Magnetoencephalography in a memory paradigm assessing correct rejection (CR) of lures, item recognition (IR) and associative recall (AR) in human participants of both sexes. We found that power decreases in the alpha frequency band (10-12 Hz) systematically track different mnemonic outcomes in both time and space: Over left posterior sensors, alpha power decreased in a stepwise fashion from 500 ms onward, first from CR to IR and then from IR to AR. When projecting alpha power into source space, the CRN known from fMRI studies emerged, including posterior parietal cortex (PPC) and hippocampus. While PPC showed a monotonic change across conditions, hippocampal effects were specific to recall. These region-specific effects were corroborated by a separate fMRI dataset. Importantly, alpha power time courses revealed a temporal dissociation between item and associative memory in hippocampus and PPC, with earlier AR effects in hippocampus. Our data thus link engagement of the CRN to the temporal dynamics of episodic memory and highlight the role of alpha rhythms in revealing when and where different types of memories are retrieved. Our ability to remember ranges from the vague feeling of familiarity to vivid recollection of associated details. Scientific understanding of episodic memory thus far relied upon separate lines of research focusing on either temporal (via electroencephalography) or spatial (via functional magnetic resonance imaging) dimensions. However, both techniques have limitations that have hindered understanding of when and where memories are retrieved. Capitalizing on the enhanced temporal and spatial resolution of magnetoencephalography, we show that changes in alpha power reveal both when and where different types of memory are retrieved. Having access to the temporal and spatial characteristics of successful retrieval provided new insights into the cross-regional dynamics in the hippocampus and parietal cortex.
Topics: Adolescent; Adult; Alpha Rhythm; Association Learning; Brain Mapping; Female; Hippocampus; Humans; Magnetoencephalography; Male; Mental Recall; Nerve Net; Parietal Lobe; Psychomotor Performance; Recognition, Psychology; Young Adult
PubMed: 32034067
DOI: 10.1523/JNEUROSCI.1982-19.2020 -
The Journal of Physiology Oct 2014Acetylcholine is a crucial neuromodulator for attention, learning and memory. Release of acetylcholine in primary sensory cortex enhances processing of sensory stimuli,... (Review)
Review
Acetylcholine is a crucial neuromodulator for attention, learning and memory. Release of acetylcholine in primary sensory cortex enhances processing of sensory stimuli, and many in vitro studies have pinpointed cellular mechanisms that could mediate this effect. In contrast, how cholinergic modulation shapes the function of intact circuits during behaviour is only beginning to emerge. Here we review recent data on the recruitment of identified interneuron types in neocortex by cholinergic signalling, obtained with a combination of genetic targeting of cell types, two-photon imaging and optogenetics. These results suggest that acetylcholine release during basal forebrain stimulation, and during physiological recruitment of the basal forebrain, can strongly and rapidly influence the firing of neocortical interneurons. In contrast to the traditional view of neuromodulation as a relatively slow process, cholinergic signalling can thus rapidly convey time-locked information to neocortex about the behavioural state of the animal and the occurrence of salient sensory stimuli. Importantly, these effects strongly depend on interneuron type, and different interneuron types in turn control distinct aspects of circuit function. One prominent effect of phasic acetylcholine release is disinhibition of pyramidal neurons, which can facilitate sensory processing and associative learning.
Topics: Acetylcholine; Animals; Association Learning; Interneurons; Neocortex
PubMed: 24879871
DOI: 10.1113/jphysiol.2014.273862 -
Current Opinion in Neurobiology Apr 2010Although fear research has largely focused on the amygdala, recent findings highlight cortical control of the amygdala in the service of fear regulation. In rodent... (Review)
Review
Although fear research has largely focused on the amygdala, recent findings highlight cortical control of the amygdala in the service of fear regulation. In rodent models, it is becoming well established that the infralimbic (IL) prefrontal cortex plays a key role in extinction learning, and recent findings are uncovering molecular mechanisms involved in extinction-related plasticity. Furthermore, mounting evidence implicates the prelimbic (PL) prefrontal cortex in the production of fear responses. Both IL and PL integrate inputs from the amygdala, as well as other structures to gate the expression of fear via projections to inhibitory or excitatory circuits within the amygdala. We suggest that dual control of the amygdala by separate prefrontal modules increases the flexibility of an organism's response to danger cues.
Topics: Affect; Amygdala; Animals; Association Learning; Behavior; Extinction, Psychological; Fear; Humans; Neural Pathways; Neuronal Plasticity; Prefrontal Cortex
PubMed: 20303254
DOI: 10.1016/j.conb.2010.02.005 -
Acta Neurobiologiae Experimentalis 1988Organization of intrinsic connections of the frontal association cortex (FAC) in dogs was studied using retrograde HRP-transport method. For cytoarchitectonic...
Organization of intrinsic connections of the frontal association cortex (FAC) in dogs was studied using retrograde HRP-transport method. For cytoarchitectonic observations and measurements of thickness of the cortex and its particular layers, additional sections stained with Nissl method were examined. Organization of intrinsic connections showed that within the dog's FAC two main cortical zones could be distinguished - the dorsal and the ventral one. The dorsal zone involves dorsally situated areas on the lateral and medial aspects of the hemisphere, which belong to the prefrontal and premotor regions. The vientral zone consists only of prefrontal areas situated ventrally on both aspects of the hemisphere. Each of the zones is characterized by strong mutual intrinsic connections and weak connections with the other zone. At the border there is a transitional area in which connections from both dorsal and ventral zones overlap. The cytoarchitectonic observations indicated that the dorsal and ventral zones can be distinguished in the central and caudal, but not in the rostral FAC subregion. The dorsal zone is characterized by considerable thickness of the cortex, cortical layers III and V, and the presence in these layers of scattered, large pyramidal neurons. The ventral zone has thinner cortex and layers III and V, and their pyramidal neurons are more uniform in size. In none of the zones clearly defined granular layer IV was observed.
Topics: Animals; Association; Brain Mapping; Dogs; Frontal Lobe; Horseradish Peroxidase
PubMed: 3188998
DOI: No ID Found -
The Journal of Neuroscience : the... Sep 2015Rewards obtained from specific behaviors can and do change across time. To adapt to such conditions, humans need to represent and update associations between behaviors...
Rewards obtained from specific behaviors can and do change across time. To adapt to such conditions, humans need to represent and update associations between behaviors and their outcomes. Much previous work focused on how rewards affect the processing of specific tasks. However, abstract associations between multiple potential behaviors and multiple rewards are an important basis for adaptation as well. In this experiment, we directly investigated which brain areas represent associations between multiple tasks and rewards, using time-resolved multivariate pattern analysis of functional magnetic resonance imaging data. Importantly, we were able to dissociate neural signals reflecting task-reward associations from those related to task preparation and reward expectation processes, variables that were often correlated in previous research. We hypothesized that brain regions involved in processing tasks and/or rewards will be involved in processing associations between them. Candidate areas included the dorsal anterior cingulate cortex, which is involved in associating simple actions and rewards, and the parietal cortex, which has been shown to represent task rules and action values. Our results indicate that local spatial activation patterns in the inferior parietal cortex indeed represent task-reward associations. Interestingly, the parietal cortex flexibly changes its content of representation within trials. It first represents task-reward associations, later switching to process tasks and rewards directly. These findings highlight the importance of the inferior parietal cortex in associating behaviors with their outcomes and further show that it can flexibly reconfigure its function within single trials. Significance statement: Rewards obtained from specific behaviors rarely remain constant over time. To adapt to changing conditions, humans need to continuously update and represent the current association between behavior and its outcomes. However, little is known about the neural representation of behavior-outcome associations. Here, we used multivariate pattern analysis of functional magnetic resonance imaging data to investigate the neural correlates of such associations. Our results demonstrate that the parietal cortex plays a central role in representing associations between multiple behaviors and their outcomes. They further highlight the flexibility of the parietal cortex, because we find it to adapt its function to changing task demands within trials on relatively short timescales.
Topics: Adult; Association Learning; Female; Humans; Male; Parietal Lobe; Reward
PubMed: 26354905
DOI: 10.1523/JNEUROSCI.4882-14.2015 -
The Journal of Neuroscience : the... Aug 2018Perception can be cast as a process of inference, in which bottom-up signals are combined with top-down predictions in sensory systems. In line with this, neural...
Perception can be cast as a process of inference, in which bottom-up signals are combined with top-down predictions in sensory systems. In line with this, neural activity in sensory cortex is strongly modulated by prior expectations. Such top-down predictions often arise from cross-modal associations, such as when a sound (e.g., bell or bark) leads to an expectation of the visual appearance of the corresponding object (e.g., bicycle or dog). We hypothesized that the hippocampus, which rapidly learns arbitrary relationships between stimuli over space and time, may be involved in forming such associative predictions. We exposed male and female human participants to auditory cues predicting visual shapes, while measuring high-resolution fMRI signals in visual cortex and the hippocampus. Using multivariate reconstruction methods, we discovered a dissociation between these regions: representations in visual cortex were dominated by whichever shape was presented, whereas representations in the hippocampus reflected only which shape was predicted by the cue. The strength of hippocampal predictions correlated across participants with the amount of expectation-related facilitation in visual cortex. These findings help bridge the gap between memory and sensory systems in the human brain. The way we perceive the world is to a great extent determined by our prior knowledge. Despite this intimate link between perception and memory, these two aspects of cognition have mostly been studied in isolation. Here we investigate their interaction by asking how memory systems that encode and retrieve associations can inform perception. We find that upon hearing a familiar auditory cue, the hippocampus represents visual information that had previously co-occurred with the cue, even when this expectation differs from what is currently visible. Furthermore, the strength of this hippocampal expectation correlates with facilitation of perceptual processing in visual cortex. These findings help bridge the gap between memory and sensory systems in the human brain.
Topics: Adult; Association; Association Learning; Cues; Female; Form Perception; Hippocampus; Humans; Magnetic Resonance Imaging; Male; Neuroimaging; Pattern Recognition, Physiological; Visual Cortex
PubMed: 29986875
DOI: 10.1523/JNEUROSCI.0163-18.2018