edictably with stimulus parameters, it is widely held to be the primary variable relating neuronal response to visual experience (Adrian, 1928; Lettvin et al., 1959; Werner and Mountcastle, 1963; Barlow, 1972; Henry et al., 1973). Accordingly, many studies hold a stimulus parameter constant during an experiment, measure large variations in firing frequency across different trials and high within-trial variation in inter-spike intervals, and conclude that the microstructure of spike trains is essentially random (Schiller et al., 1976; Heggelund and Albus, 1978; Tolhurst et al., 1981; Tolhurst et al., 1983; Vogels et al., 1989; Softky and Koch, 1993; Shadlen and Newsome, 1994). A few studies have emphasized that cells in mammalian visual cortex responding to moving patterns show stimulus-locked temporal modulation, sometimes referred to as "grain" response (Tomko and Crapper, 1974; Hammond and MacKay, 1977; Gulyas et al., 1987; Snowden et al., 1992). However, the time scale and stimulus

mutal Slovin, and Moshe Abeles. Spatiotemporal structure of millisecond time scale. cortical activity: properties and behavioral relevance. J. Neuro- The single neuron time-dependent rate function was taken physiol. 79: 2857–2874, 1998. The study was designed to reveal by many as the coding parameter (e.g., Barlow 1972, 1992, occurrences of precise firing sequences (PFSs) in cortical activity and to test their behavioral relevance. Two monkeys were trained 1994; Newsome et al. 1989; Rolls 1991). Others suggested to perform a delayed-response paradigm and to open puzzle boxes. a population coding, based on either the summed activity of Extracellular activity was recorded from neurons in premotor and neurons (Georgopoulos et al. 1986; Schwartz 1994), or the prefrontal areas with an array of six microelectrodes. An algorithm coherency in firing among cells (Eckhorn et al. 1988; Engel was developed to detect PFSs, defined as a set of three spikes and et al. 1991a–c; Gray and Singer 1992; Gray et al. 1989, two intervals with a precision of {1 ms repeating significantly 1992). Both views ignored the detailed temporal structure more than expected by chance. The expected level of repetition of cortical activity, assuming that precision is not compatible was computed based on the firing rate and the pairwise correlation with a noisy cortical environment. Despite this notion, sevof

We outline the rationale and preliminary results of using the State Context Property (SCOP) formalism, originally developed as a generalization of quantum mechanics, to describe the contextual manner in which concepts are evoked, used, and combined to generate meaning. The quantum formalism was developed to cope with problems arising in the description of (1) the measurement process, and (2) the generation of new states with new properties when particles become entangled. Similar problems arising with concepts motivated the formal treatment introduced here. Concepts are viewed not as fixed representations, but entities existing in states of potentiality that require interaction with a context—a stimulus or another concept—to ‘collapse ’ to an instantiated form (e.g. exemplar, prototype, or other possibly imaginary instance). The stimulus situation plays the role of the measurement in physics, acting as context that induces a change of the cognitive state from superposition state to collapsed state. The collapsed state is more likely to consist of a conjunction of concepts for associative than analytic thought because more stimulus or concept properties take part in the collapse. We provide two contextual measures of conceptual distance—one using collapse probabilities and the other weighted properties—and show how they can be applied to conjunctions using the pet fish problem.

It is not clear how information related to cognitive or psychological processes is carried by or represented in the responses of single neurons. One provocative proposal is that precisely timed spike patterns play a role in carrying such information. This would require that these spike patterns have the potential for carrying information that would not be available from other measures such as spike count or latency. We examined exactly timed (1-ms precision) triplets and quadruplets of spikes in the stimulus-elicited responses of lateral geniculate nucleus (LGN) and primary visual cortex (V1) neurons of the awake fixating rhesus monkey. Large numbers of these precisely timed spike patterns were found. Information theoretical analysis showed that the precisely timed spike patterns carried only information already available from spike count, suggesting that the number of precisely timed spike

: In this work we discuss Hebb's old ideas about cell assemblies in the light of recent results concerning temporal structure and correlations in neural signals. We want to give a conceptual, necessarily only rough picture, how ideas about `binding by synchronisation', `synfire chains', `local and global assemblies', `short and long term memory' and `behaviour' might be integrated into a coherent model of brain functioning based on neuronal assemblies. Keywords: cell assemblies, synchronization, gamma-oscillations, synfire chains, memory, behaviour 1 ASSEMBLIES AND ASSOCIATIVE MEMORIES 1.1 Cell Assemblies Cell assemblies have been introduced by Donald Hebb with the intention of providing a functional and at the same time structural model for cortical processes and neuronal representations of external events (Hebb, 1949). According to Hebb's ideas, stimuli, objects, things, but also more abstract entities like concepts, contextual relations, ideas, and so on are thought of being repre...

Abstract: Fundamental approaches bypass the problem of getting consciousness from non-conscious components by positing that consciousness is a universal primitive. For example, the double aspect theory of information holds that information has a phenomenal aspect. How then do you get from phenomenal information to human consciousness? This paper proposes that an entity is conscious to the extent it amplifies information, first by trapping and integrating it through closure, and second by maintaining dynamics at the edge of chaos through simultaneous processes of divergence and convergence. The origin of life through autocatalytic closure, and the origin of an interconnected worldview through conceptual closure, induced phase transitions in the degree to which information, and thus consciousness, is locally amplified. Divergence and convergence of cognitive information may involve phenomena observed in light e.g. focusing, interference, and resonance. By making information flow inward- biased, closure shields us from external consciousness; thus the paucity of consciousness may be an illusion.

You might find this additional information useful... This article cites 33 articles, 19 of which you can access free at:

Visual processing shows a highly distributed organization in which the presentation of a visual stimulus simultaneously activates neurons in multiple columns across several cortical areas. It has been suggested that precise spatiotemporal activity patterns within and across cortical areas play a key role in higher cognitive, motor, and visual functions. In the visual system, these patterns have been proposed to take part in binding stimulus features into a coherent object, i.e., to be involved in perceptual grouping. Using voltagesensitive dye imaging (VSDI) in behaving monkeys (Macaca fascicularis, males), we simultaneously measured neural population activity in the primary visual cortex (V1) and extrastriate cortex (V2, V4) at high spatial and temporal resolution. We detected time point population events (PEs) in the VSDI signal of each pixel and found that they reflect transient increased neural activation within local populations by establishing their relation to spiking and local field potential activity. Then, we searched for repeating space and time relations between the detected PEs. We demonstrate the following: (1) spatiotemporal patterns occurring within (horizontal) and across (vertical) early visual areas repeat significantly above chance level; (2) information carried in only a few patterns can be used to reliably discriminate between stimulus categories on a single-trial level; (3) the spatiotemporal patterns yielding high classification performance are characterized by late temporal occurrence and top-down propagation, which are consistent with cortical mechanisms involving perceptual grouping. The pattern characteristics and the robust relation between the patterns and the stimulus categories suggest that

This paper outlines a taxonomy of neural pulse codes and reviews neurophysiological evidence for interspike interval-based representations for pitch and timbre in the auditory nerve and cochlear nucleus. Neural pulse codes can be divided into channel-based codes, temporal-pattern codes, and time-of-arrival codes. Timings of discharges in auditory nerve fibers reflect the time structure of acoustic waveforms, such that the interspike intervals that are produced precisely convey information concerning stimulus periodicities. Population-wide inter-spike interval distributions are constructed by summing together intervals from the observed responses of many single Type I auditory nerve fibers. Features in such distributions correspond closely with pitches that are heard by human listeners. The most common allorder interval present in the auditory nerve array almost invariably corresponds to the pitch frequency, whereas the relative fraction of pitchrelated intervals amongst all others qualitatively corresponds to the strength of the pitch. Consequently, many diverse aspects of pitch perception are explained in terms of such temporal representations. Similar stimulus-driven temporal discharge patterns are observed in major neuronal populations of the cochlear nucleus. Population-interval distributions constitute an alternative time-domain strategy for Reprint address: