Effects of enkephalins on associative processes of parietal cortex neurons

Experiments on cats examined the effect of met- and leu-enkephalins on the process of learning of the parietal associative cortex neurons (field 5). It has been shown that conditioned electrical stimulation of the pyramidal tract axons with nociceptive reinforcement evoked plastic changes of responses in 35 neurons. It was found that the effect of microiontophoretically applied enkephalins on these neurons depend on the time of iontophoretic application. When endogenous opioid peptides were applied up to 30-40 min they inhibited the process of elaboration of temporary connection.     

Unit and focal responses of the parietal associative cortex to peripheral stimulation

Unit and focal responses arising in the parietal associative region (anterior part of the middle suprasylvian gyrus) to various forms of peripheral stimulation were investigated in acute experiments on cats anesthetized by intraperitoneal injection of chloralose (40 mg/kg) and pentobarbital (20 mg/kg). Under these conditions focal potentials of the associative response (AR) type appear. They consist of three components: negative, positive, and negative. The positive and second negative components have their polarity changed as the recording electrode is inserted to a depth of 1200–1500 µ. Two types of unit responses related to the development of the positive and negative phases are distinguished. This applies to responses of both monosensory and polysensory neurons, and even the same neuron may give responses of both first and second types because of their unstable latent period. In the case of intracellular or "partial intracellular" recording, excitatory and inhibitory postsynaptic potentials (EPSPs and IPSPs) corresponding to the first and second types of responses were observed, so that the total unit response had the form of an EPSP-IPSP-EPSP-IPSP sequence. With most neurons whose activity was recorded in this way the first EPSP and IPSP were not observed.State Medical Institute, Kemerovo. Translated from Neirofiziologiya, Vol.4, No.4, pp. 358–367, July–August, 1972.     

Modality-specific control of strategic spatial attention in parietal cortex

The neural basis of selective spatial attention presents a significant challenge to cognitive neuroscience. Recent neuroimaging studies have suggested that regions of the parietal and temporal cortex constitute a "supramodal" network that mediates goal-directed attention in multiple sensory modalities. Here we used transcranial magnetic stimulation (TMS) to determine which cortical subregions control strategic attention in vision and touch. Healthy observers undertook an orienting task in which a central arrow cue predicted the location of a subsequent visual or somatosensory target. To determine the attentional role of cortical subregions at different stages of processing, TMS was delivered to the right hemisphere during cue or target events. Results indicated a critical role of the inferior parietal cortex in strategic orienting to visual events, but not to somatosensory events. These findings are inconsistent with the existence of a supramodal attentional network and instead provide direct evidence for modality-specific attentional processing in parietal cortex.     

Role of the parietal associative cortex in "counting" behavior of dogs

Influence of the combined and isolated lesions of areas 5 and 7 of the parietal cortex on the counting behavior was studied in experiments with 6 dogs. Instrumental feeding reaction (lifting and placing the forepaw on the foodwell) was established. The positive conditioned stimulus was a series of 5 clicks with variable interclicks intervals and the negative (non-reinforced) conditioned stimulus was a series of 3 clicks, so that asymmetrical differentiation was elaborated. Combined bilateral lesions of areas 5 and 7 and an isolated lesion of area 5 resulted in a severe impairment of the numerical discrimination for two months, whereas the isolated lesion of area 7 did not lead to any problems in differentiation. The conclusion was made that area 5 is critical for numerical discrimination of sequential stimuli.     

Multimodal spatial representations engaged in human parietal cortex during both saccadic and manual spatial orienting

BACKGROUND: Recent neuroimaging studies have found that several areas of the human brain, including parietal regions, can respond multimodally. But given single-cell evidence that responses in primate parietal cortex can be motor-related, some of the human multimodal activations might reflect convergent activation of potentially motor-related areas, rather than multimodal representations of space independent of motor factors. Here we crossed sensory stimulation of different modalities (vision or touch, in left or right hemifield) with spatially directed responses to such stimulation by different effector-systems (saccadic or manual). RESULTS: The fMRI results revealed representations of contralateral space in both the posterior part of the superior parietal gyrus and the anterior intraparietal sulcus that activated independently of both sensory modality and motor response. Multimodal saccade-related or manual-related activations were found, by contrast, in different regions of parietal cortex. CONCLUSIONS: Whereas some parietal regions have specific motor functions, others are engaged during the execution of movements to the contralateral hemifield irrespective of both input modality and the type of motor effector.     

Dynamics of parietal neural activity during spatial cognitive processing

Dynamic neural processing unrelated to changes in sensory input or motor output is likely to be a hallmark of cognitive operations. Here we show that neural representations of space in parietal cortex are dynamic while monkeys perform a spatial cognitive operation on a static visual stimulus. We recorded neural activity in area 7a during a visual maze task in which monkeys mentally followed a path without moving their eyes. We found that the direction of the followed path could be recovered from neuronal population activity. When the monkeys covertly processed a path that turned, the population representation of path direction shifted in the direction of the turn. This neural population dynamic took place during a period of unchanging visual input and showed characteristics of both serial and parallel processing. The data suggest that the dynamic evolution of parietal neuronal activity is associated with the progression of spatial cognitive operations.     

Abnormal attentional modulation of retinotopic cortex in parietal patients with spatial neglect

Brain regions beyond visual cortex are thought to be responsible for attention-related modulation of visual processing [1, 2], but most evidence is indirect. Here, we applied functional magnetic resonance imaging (fMRI), including retinotopic mapping of visual areas, to patients with focal right-parietal lesions and left spatial neglect [3, 4]. When attentional load at fixation was minimal, retinotopic areas in right visual cortex showed preserved responses to task-irrelevant checkerboards in the contralateral left hemifield, analogously to left visual cortex for right-hemifield checkerboards, indicating a "symmetric" pattern in both hemispheres with respect to contralateral stimulation under these conditions. But when attentional load at fixation was increased, a functional asymmetry emerged for visual cortex, with contralateral responses in right visual areas being pathologically reduced (even eliminated for right V4/TEO), whereas left visual areas showed no such reduction in their contralateral response. These results reveal attention-dependent abnormalities in visual cortex after lesions in distant (parietal) regions. This may explain otherwise puzzling aspects of neglect [5, 6], as confirmed here by additional behavioral testing.     

Genesis of different components of evoked response in the associative parietal cortex of the cat's brain

The responses evoked in the associative parietal region of the brain by different peripheral stimuli constitute a complex reaction. An early short-latent component of the associative response (ECAR) is formed as the result of specific afferentation, whereas the long-latent late component that follows it is evoked by pulsations from nonspecific, reticular, and associative nuclei in the thalamus or by pulsations arriving from specific nuclei by indirect routes. The cortical mechanisms whereby ECAR arise may be provided by the structural-organization characteristics of interneuronal connections, in particular by the presence in all cortical layers of the terminals of afferent fibers, which establish contact that are mainly axodendritic.Institute of Normal and Pathological Physiology, Academy of Medical Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 2, No. 4, pp. 399–405, July–August, 1970.     

Interaction between impulses evoked by stimuli of different modalities in neurons of the parietal associative cortex

In acute experiments on cats anesthetized with chloralose and nembutal interaction between visual, auditory, and electrodermal stimuli in neurons of the parietal association cortex was studied. Two types of interaction were found; the first characterized by inhibition or by inhibition followed by facilitation of the response to the test stimulus, the second by facilitation or by facilitation followed by inhibition of spontaneous impulses. Interaction between stimuli of different modalities was shown to depend on the properties of the neuron. In polysensory neurons ability to interact was much higher than in bimodal or monomodal neurons.M. Gorkii Donetsk Medical Institute. Kemerovo Medical Institute. Translated from Neirofiziologiya, Vol. 8, No. 3, pp. 223–229, May–June, 1976.     

Distribution of specific signals of different modality in the associative parietal area of the cat cortex

In cats under nembutal anesthesia eliciting specific early components of association responses, the drug parietal distribution upon forepaw and thalamic stimulation was studied: relay somatic-ventrobasal complex (VB) and association nuclei, transmitting specific visual impulses in pulvinar (Pul) and lateral-posterior (LP) areas. Signals of maximum intensity were observed in response to peripheral and central stimulation near somatic area and in response to Pul and LP stimulation in the medial part of parietal cortex. Besides, a general principle revealing more intensive signals of different modality in the areas near lateral sulcus than in other parietal areas was established. The difference in processing of specific polysensory signals in various parietal areas and consequently, different involvement of the latter into the systemic action of the brain was proved, this being related to the character of topical organization of these signals.     

Effect of damage to the parietal associative cortex on the function of acquired motor coordination in dogs

The effect of ablation of the parietal associative cortex on the performance of a complex food instrumental reaction was studied in dogs. The reaction consisted in two movements of the forelimb which were of similar pattern, but differed by their coordination. The first one was the lifting and holding of the paw at a required level for a required time, with the head in natural position (lifted), and the second one was the same movement of the paw with the head bent down for feeding, i.e. a new coordination, for the natural coordination consists in lowering of the forelimb associated with lowering of the head. During two sessions after the lesion, both reactions became irregular (so that the dogs performed only one of two movements or none). In the course of four months, the precision of the first movement was reduced, the amplitude of lifting the paw and duration of holding it were diminished. The new coordination persisted after ablation of the parietal associative cortex, though the holding (fixation) of the paw was less perfect. As was shown before by one of the present authors (M. E. Ioffe), lesion of the sensorimotor cortex resulted in profound disturbance of acquired coordination.     

Human parietal cortex in action

Experiments using functional neuroimaging and transcranial magnetic stimulation in humans have revealed regions of the parietal lobes that are specialized for particular visuomotor actions, such as reaching, grasping and eye movements. In addition, the human parietal cortex is recruited by processing and perception of action-related information, even when no overt action occurs. Such information can include object shape and orientation, knowledge about how tools are employed and the understanding of actions made by other individuals. We review the known subregions of the human posterior parietal cortex and the principles behind their organization.