The cognitive significance of resonating neurons in the cerebral cortex

Most neural fibers of the cerebral cortex engage in electric signaling, but one particular fiber, the apical dendrite of the pyramidal neuron, specializes in electric resonating. This dendrite extends upward from somas of pyramidal neurons, the most numerous neurons of the cortex. The apical dendrite is embedded in a recurrent corticothalamic circuit that induces surges of electric current to move repeatedly down the dendrite. Narrow bandwidths of surge frequency (resonating) enable cortical circuits to use specific carrier frequencies, which isolate the processing of those circuits from other circuits. Resonating greatly enhances the intensity and duration of electrical activity of a neuron over a narrow frequency range, which underlies attention in its various modes. Within the minicolumn, separation of the central resonating circuit from the surrounding signal processing network separates “having” subjective impressions from “thinking about” them. Resonating neurons in the insular cortex apparently underlie cognitive impressions of feelings.     

Electrical potentials of the cerebral cortex and psychometric intelligence

Contradictory findings concerning relationships between intelligence-test scores and different EEG evoked-potential (EP) measures have been reported. The positive findings suggest that intelligence is correlated with the number and amplitude of components in the EP waveform. Since there is evidence that both of these parameters are influenced by stimulus intensity, we examined the extent to which an EP/intelligence relationship may depend on stimulus intensity. In a sample of 22 Ss a relationship between EP amplitude and intelligence was found and the magnitude of this correlation was related systematically to stimulus intensity. The maximum correlation (r = 0.69) with scores on the Raven's Advanced Progressive Matrices was obtained at an intermediate level of intensity. These findings may account for some of the inconsistencies in the literature. Moreover, they suggest an explanation for higher general intelligence in terms of greater central activation of neural processes in response to normal levels of stimulation.     

A role for the anterior insular cortex in the global neuronal workspace model of consciousness

According to the global neuronal workspace model of consciousness, consciousness results from the global broadcast of information throughout the brain. The global neuronal workspace is mainly constituted by a fronto-parietal network. The anterior insular cortex is part of this global neuronal workspace, but the function of this region has not yet been defined within the global neuronal workspace model of consciousness. In this review, I hypothesize that the anterior insular cortex implements a cross-modal priority map, the function of which is to determine priorities for the processing of information and subsequent entrance in the global neuronal workspace.     

The role of neuronal signaling in controlling cerebral blood flow

Well-regulated blood flow within the brain is vital to normal function. The brain's requirement for sufficient blood flow is ensured by a tight link between neural activity and blood flow. The link between regional synaptic activity and regional cerebral blood flow, termed functional hyperemia, is the basis for several modern imaging techniques that have revolutionized the study of human brain activity. Here, we review the mechanisms of functional hyperemia and their implications for interpreting the blood oxygen level-dependent (BOLD) contrast signal used in functional magnetic resonance imaging (fMRI).     

Dynamics of the cerebral cortex automatic development of equilibrium in self-organizing systems

The nervous system, and particularly the cerebral cortex, is examined in certain of its activities, it being treated as a purely physical dynamic system. It is shown mathematically that if, as seems likely, the cerebral cortex can undergo manifold changes of neuronic organization, then it follows that these changes must automatically lead to the development of more and more states of equilibrium, the process being unavoidable and largely irreversible. The theorem may be established on basic physical principles without appeal to special physiological details. The possible significance of this observation is indicated.     

Neural correlates of partial transmission of sensorimotor information in the cerebral cortex

Using single neuron recordings in monkey primary motor (MI) cortex, two series of experiments were conducted in order to know whether response preparation can begin before perceptual processing finishes, thus providing evidence for a temporal overlap of perceptual and motor processes.

In Experiment 1, a “left/right, Go/No-Go” reaction time (RT) task was used. One monkey was trained to perform wrist flexion/extension movements to align a pointer with visual targets. The visual display was organized to provide a two-dimensional stimulus: side (an easy discrimination between left and right targets) which determined movement direction, and distance (a difficult discrimination between distal and proximal targets) which determined whether or not the movement was to be made. Changes in neuronal activity, when they were time-locked to the stimulus, were almost similar in the Go and No-Go trials, and when they were time-locked to movement onset, were markedly reduced in No-Go as compared to Go trials.

In Experiment 2, a stimulus-response compatibility (SRC) task was used. Two monkeys were trained to align a pointer with visual targets, on either left or right. In the spatially “compatible” trials, they had to point at the stimulus position, whereas in the “incompatible” trials, they had to point at the target located in the opposite side. For 12.5% of neurons, changes in activity associated with incompatible trials looked like changes in activity associated with movements performed in the opposite direction during compatible trials, thus suggesting the hypothesis of an automatic activation of the congruent, but incorrect response.

Results of both experiments provide evidence for a partial transmission of information from visual to motor cortical areas: that is, in the No-Go trials of the first task, information about movement direction, before the decision to perform or not this movement was made, and, in the incompatible trials of the SRC task, information about the congruent, but incorrect response, before the incongruent, but correct response was programmed.     

The basolateral amygdala modulates specific sensory memory representations in the cerebral cortex

Stress hormones released by an experience can modulate memory strength via the basolateral amygdala, which in turn acts on sites of memory storage such as the cerebral cortex [McGaugh, J. L. (2004). The amygdala modulates the consolidation of memories of emotionally arousing experiences. Annual Review of Neuroscience, 27, 1–28]. Stimuli that acquire behavioral importance gain increased representation in the cortex. For example, learning shifts the tuning of neurons in the primary auditory cortex (A1) to the frequency of a conditioned stimulus (CS), and the greater the level of CS importance, the larger the area of representational gain [Weinberger, N. M. (2007). Associative representational plasticity in the auditory cortex: A synthesis of two disciplines. Learning & Memory, 14(1–2), 1–16]. The two lines of research suggest that BLA strengthening of memory might be accomplished in part by increasing the representation of an environmental stimulus. The present study investigated whether stimulation of the BLA can affect cortical memory representations. In male Sprague–Dawley rats studied under urethane general anesthesia, frequency receptive fields were obtained from A1 before and up to 75 min after the pairing of a tone with BLA stimulation (BLAstm: 100 trials, 400 ms, 100 Hz, 400 μA [±16.54]). Tone started before and continued after BLAstm. Group BLA/1.0 (n = 16) had a 1 s CS–BLAstm interval while Group BLA/1.6 (n = 5) has a 1.6 s interval. The BLA/1.0 group did develop specific tuning shifts toward and to the CS, which could change frequency tuning by as much as two octaves. Moreover, its shifts increased over time and were enduring, lasting 75 min. However, group BLA/1.6 did not develop tuning shifts, indicating that precise CS–BLAstm timing is important in the anesthetized animal. Further, training in the BLA/1.0 paradigm but stimulating outside of the BLA did not produce tuning shifts. These findings demonstrate that the BLA is capable of exerting highly specific, enduring, learning-related modifications of stimulus representation in the cerebral cortex. These findings suggest that the ability of the BLA to alter specific cortical representations may underlie, at least in part, the modulatory influence of BLA activity on strengthening long-term memory.     

Effects of preliminary perceptual output on neuronal activity of the primary motor cortex.

Observations of single neurons in the primary motor cortex of 1 monkey provided evidence that preliminary perceptual information reaches the motor system before perceptual analysis is complete. Neurons were recorded during a task in which 1 stimulus was assigned to a wrist flexion response and another was assigned to wrist extension. Two stimuli were assigned to a no-go response; each was visually similar to either the flexion or the extension stimulus. When a no-go stimulus was presented, neurons responded with weaker versions of the discharge patterns exhibited to the visually similar stimulus requiring a movement, suggesting that neurons receive partial perceptual information favoring that movement. Functionally separable neuronal populations were identified, and differences in the activations of these provide evidence about the functional effects of preliminary perceptual output on movement control processes.