Experiments were made on the posterior parietal association cortical areas 5 and in 17 hemispheres of 11 monkeys, 6 M. mulatta and 5 M. arctoides. The electrical signs of the activity of single cortical cells were recorded with microelectrodes in waking animals as they carried out certain behavioral acts in response to a series of sensory cues. The behavioral paradigms were one for detection alone, and a second for detection plus projection of the arm to contact a stationary or moving target placed at arm's length. Of the 125 microelectrode penetrations made, 1,451 neurons were identified in terms of the correlation of their activity with the behavioral acts and their sensitivity or lack of it to sensory stimuli delivered passively; 180 were studied quantitatively. The locations of cortical neurons were identified in serial sections; 94 penetrations and 1,058 neurons were located with certainty. About two-thirds of the neurons of area 5 were activated by passive rotation of the limbs at their joints; of these, 82% were related to single, contralateral joints, 10% to two or more contralateral joints, 6% to ipsilateral, and 2% to joints on both sides of the body. A few of the latter were active during complex bodily postures. A large proportion of area 5 neurons were relatively insensitive to passive joint rotations, as compared with similar neurons of the postcentral gyrus, but were driven to high rates of discharge when the same joint was rotated during an active movement of the animal...

Posterior parietal association cortex of the monkey: command functions for operations within extrapersonal space

http://web.mit.edu/~ppurdon/www/source-imaging.pdf

EEG source imaging

An overview of the following six cortical zones that have been defined in the presurgical evaluation of candidates for epilepsy surgery is given: the symptomatogenic zone; the irritative zone; the seizure onset zone; the epileptogenic lesion; the epileptogenic zone; and the eloquent cortex. The stepwise historical evolution of these different zones is described. The current diagnostic techniques used in the definition of these cortical zones, such as video-EEG monitoring, MRI and ictal single photon emission computed tomography, are discussed. Established diagnostic tests are set apart from procedures that should still be regarded as experimental, such as magnetoencephalography, dipole source localization and spike-triggered functional MRI. Possible future developments that might lead to a more direct definition of the epileptogenic zone are presented.

/pdf/presurgical-evaluation-of-epilepsy-216chlpgp2.pdf

Presurgical evaluation of epilepsy.

When we look at our hands, we immediately know that they are part of our own body. This feeling of ownership of our limbs is a fundamental aspect of self-consciousness. We have studied the neuronal counterparts of this experience. A perceptual illusion was used to manipulate feelings of ownership of a rubber hand presented in front of healthy subjects while brain activity was measured by functional magnetic resonance imaging. The neural activity in the premotor cortex reflected the feeling of ownership of the hand. This suggests that multisensory integration in the premotor cortex provides a mechanism for bodily self-attribution.

https://science.sciencemag.org/content/sci/305/5685/875.full.pdf

That's My Hand! Activity in Premotor Cortex Reflects Feeling of Ownership of a Limb

Developing networks follow common rules to shift from silent cells to coactive networks that operate via thousands of synapses. This review deals with some of these rules and in particular those concerning the crucial role of the neurotransmitter gamma-aminobuytric acid (GABA), which operates primarily via chloride-permeable GABA(A) receptor channels. In all developing animal species and brain structures investigated, neurons have a higher intracellular chloride concentration at an early stage leading to an efflux of chloride and excitatory actions of GABA in immature neurons. This triggers sodium spikes, activates voltage-gated calcium channels, and acts in synergy with NMDA channels by removing the voltage-dependent magnesium block. GABA signaling is also established before glutamatergic transmission, suggesting that GABA is the principal excitatory transmitter during early development. In fact, even before synapse formation, GABA signaling can modulate the cell cycle and migration. The consequence of these rules is that developing networks generate primitive patterns of network activity, notably the giant depolarizing potentials (GDPs), largely through the excitatory actions of GABA and its synergistic interactions with glutamate signaling. These early types of network activity are likely required for neurons to fire together and thus to "wire together" so that functional units within cortical networks are formed. In addition, depolarizing GABA has a strong impact on synaptic plasticity and pathological insults, notably seizures of the immature brain. In conclusion, it is suggested that an evolutionary preserved role for excitatory GABA in immature cells provides an important mechanism in the formation of synapses and activity in neuronal networks.

GABA: A Pioneer Transmitter That Excites Immature Neurons and Generates Primitive Oscillations

The difficulties inherent in extracting clinically useful information by visual inspection alone from the massive amounts of data contained in multichannel polygraphic recordings have placed limits on the accuracy and range of utility of electroencephalography and evoked potentials. A method for condensing and summarizing the spatiotemporal information contained in recordings from multiple scalp electrodes is described. Data dimensionality is reduced and visibility increased by computer-controlled topographic mapping and display of data as color television images. Examples are given in which such brain electrical activity mapping (BEAM) (1) localizes tumors in patients with normal or nondiagnostic EEGs, (2) adds additional information to that visible on computerized axial tomography, and (3) demonstrates electrophysiological abnormalities in patients with functional lesions but normal CT scans. A sensitivity to the functional component of a neurological lesion suggests that BEAM may provide complementary information to the anatomical definition provided by the CT scan.

Brain electrical activity mapping (BEAM): a method for extending the clinical utility of EEG and evoked potential data.

Significance probability mapping: An aid in the topographic analysis of brain electrical activity

The response to cerebral hypoxia/ischemia may be different in the neonate compared to other age groups. An in vivo model was developed in the rat to determine whether there are age-dependent differences in the effects of hypoxia on electroencephalographic (EEG) activity. EEG recordings were obtained from Long Evans hooded rats deprived of oxygen at five ages: postnatal days 5 to 7, 10 to 12, 15 to 17, 25 to 27, and 50 to 60. Oxygen concentration was varied from 0, 2, 3, and 4% between animals. EEGs were recorded in all animals before, during, and at 1 hour after exposure to the hypoxic condition and at 1 to 7 days afterward in a subset of animals. All animals were deprived of oxygen until the onset of apnea and bradycardia to 20 to 40% of baseline heart rate values. Hypoxia resulted in isoelectric EEG significantly more frequently in the animals deprived of oxygen at postnatal days 25 to 27 and 50 to 60 than in the younger age groups. A highly significant effect was that the animals deprived at postnatal days 5 to 17 revealed a high incidence of epileptiform EEG activity during hypoxia. In contrast, the older animals exhibited only rare isolated EEG spikes before reaching an isoelectric EEG. The severity of hypoxia-induced epileptiform EEG changes was highest in the animals subjected to moderately hypoxic conditions (3% and 4% oxygen) at postnatal days 10 to 12. Furthermore, epileptiform changes persisted for hours to days following prolonged episodes of hypoxia in the younger animals. This study demonstrates a unique response of the immature brain to exhibit epileptiform activity during hypoxia.

Epileptogenic effect of hypoxia in the immature rodent brain

The receptive fields of single cells in area 5 of monkey parietal cortex were studied by extracellular recording. Cells were driven primarily by gentle manipulation of multiple joints residing on one or more limbs. Both excitatory and inhibitory convergence were demonstrated. It is postulated that the multijoint receptive fields of area 5 are the result of convergence from single-joint cells of the primary receiving area. An analogy is drawn between the modification of information in the visual and somatosensory systems.

https://science.sciencemag.org/content/sci/172/3980/273.full.pdf

Somatosensory System: Organizational Hierarchy from Single Units in Monkey Area 5

CATS deprived of visual experience in one eye during a critical period of early life develop marked changes in the functional organisation of their visual system1–3. Useful vision seems to be lost in the deprived eye, and neurophysiological studies reveal a loss of binocular input to neurones in the visual cortex. Most neurones fail to respond to stimuli presented to the deprived eye; whereas almost all respond to stimulation of the normal eye. In normal neonatal kittens without visual experience, most cortical neurones respond to stimulation of either eye. Moreover, this binocular neuronal input persists when subsequent visual experience is prevented by binocular lid suture. Thus, asymmetrical visual experience seems necessary to produce a loss of binocular input. This loss of functional input from the deprived eye could result from a loss of the normal excitatory synaptic connections or from inhibitory suppression of afferent input. We postulate that asymmetrical visual experience causes synaptic inhibition of input from the deprived eye and that reduction of such inhibition might restore binocularity.

James L. Burchfiel

Papers

Brain electrical activity mapping (BEAM): a method for extending the clinical utility of EEG and evoked potential data.

Significance probability mapping: An aid in the topographic analysis of brain electrical activity

Epileptogenic effect of hypoxia in the immature rodent brain

Somatosensory System: Organizational Hierarchy from Single Units in Monkey Area 5

Bicuculline reversal of deprivation amblyopia in the cat.