A spatiotemporal profile of visual system activation revealed by current source density analysis in the awake macaque

We investigated the spatiotemporal activation pattern, produced by one visual stimulus, across cerebral cortical regions in awake monkeys. Laminar profiles of postsynaptic potentials and action potentials were indexed with current source density (CSD) and multiunit activity profiles respectively. Locally, we found contrasting activation profiles in dorsal and ventral stream areas. The former, like V1 and V2, exhibit a 'feedforward' profile, with excitation beginning at the depth of Lamina 4, followed by activation of the extragranular laminae. The latter often displayed a multilaminar/columnar profile, with initial responses distributed across the laminae and reflecting modulation rather than excitation; CSD components were accompanied by either no changes or by suppression of action potentials. System-wide, response latencies indicated a large dorsal/ventral stream latency advantage, which generalizes across a wide range of methods. This predicts a specific temporal ordering of dorsal and ventral stream components of visual analysis, as well as specific patterns of dorsal-ventral stream interaction. Our findings support a hierarchical model of cortical organization that combines serial and parallel elements. Critical in such a model is the recognition that processing within a location typically entails multiple temporal components or 'waves' of activity, driven by input conveyed over heterogeneous pathways from the retina.     

M-stream deficits and reading-related visual processes in developmental dyslexia.

Some visual processing deficits in developmental dyslexia have been attributed to abnormalities in the subcortical M stream and/or the cortical dorsal stream of the visual pathways. The nature of the relationship between these visual deficits and reading is unknown. The purpose of the present article was to characterize reading-related perceptual processes that may link the visual deficits to reading problems. We identified contrast sensitivity, position encoding, oculomotor control, visual attention, parafoveal/foveal interactions, and saccadic suppression as potential reading-related dorsal stream processes. We then evaluated the role of each process in reading and the status of each process in dyslexia. In theory, a number of dorsal stream processes (e.g., oculomotor control and visual attention) might contribute to reading problems in developmental dyslexia. More work is needed to demonstrate the connection empirically. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of goal-subgoal conflict on planning ability after frontal- and temporal-lobe lesions in humans

Twenty-one patients with unilateral prefrontal cortical neurosurgical lesions (11 left and 10 right) and 38 patients with unilateral temporal lobectomy (19 left and 19 right) were compared to 44 matched control subjects on their performance on the 3-D Computerized Tower of Hanoi (3-D CTOH) test. The problems were split into those with or without a significant goal-subgoal conflict determined by whether the correct first move in each problem took the subject apparently away or towards the final goal state. The left frontal lesion and right temporal lobectomy groups were significantly impaired on problems with goal-subgoal conflicts. In the left frontal group, this deficit was confined to earlier four-move problems, whereas the right temporal group showed a more general deficit on later five-move problems. The left frontal lesion deficit is explained in terms of an inability to inhibit the response compatible with achieving a final goal, whereas the impairment in the right lesion group was related to a specific impairment in spatial memory.     

The constructive nature of vision: direct evidence from functional magnetic resonance imaging studies of apparent motion and motion imagery

Echoplanar functional magnetic resonance imaging was used to monitor activation changes of brain areas while subjects viewed apparent motion stimuli and while they were engaged in motion imagery. Human cortical areas MT (V5) and MST were the first areas of the 'dorsal' processing stream which responded with a clear increase in signal intensity to apparent motion stimuli as compared with flickering control conditions. Apparent motion of figures defined by illusory contours evoked greater activation in V2 and MT/MST than appropriate control conditions. Several areas of the dorsal pathway (V3A, MT/MST, areas in the inferior and superior parietal lobule) as well as prefrontal areas including FEF and BA 9/46 responded strongly when subjects merely imagined moving stimuli which they had seen several seconds before. The activation during motion imagery increased with the synaptic distance of an area from V1 along the dorsal processing stream. Area MT/MST was selectively activated during motion imagery but not during a static imagery control condition. The comparison between the results obtained with objective motion, apparent motion and imagined motion provides further insights into a complex cortical network of motion-sensitive areas driven by bottom-up and top-down neural processes.     

Visual control of the arm, the wrist and the fingers: pathways through the brain

Sperry and his colleagues had shown that section of the corpus callosum blocks the normally strong interocular transfer of visual learning in chiasma sectioned monkeys. Although interhemispheric transfer of learning was blocked, monkeys could be readily trained to use any combination of eye and hand in a task that required rapid visually guided responses. Sperry suggested that there must be a subcortical pathway linking sensory to motor areas of the brain. We tested monkeys in a task which required them to orient their wrist and fingers correctly in order to remove a morsel of food from a slotted disc. Animals in which we made lesions of the dorsal extrastriate visual areas of the parietal lobe were profoundly impaired in performing this task, but showed no deficit in visual discrimination learning. A monkey with an extensive lesion of the ventral, temporal lobe extrastriate areas showed no deficit in the visuomotor task but was profoundly impaired in visual discrimination learning. Lesions of peri-arcuate cortex, a major cortical target of parietal lobe visual areas, produced only a mild deficit which was motor in character. We suggest that the visuomotor deficit caused by parietal lobe lesions is brought about by depriving the cerebellum of its cortical visual input.     

Role of the dorsal prestriate cortex in visuospatial configural discrimination by monkeys

Cynomolgus monkeys (Macaca fascicularis) learned a series of visuospatial configural discriminations in which particular discriminative stimulus objects were rewarded only in particular spatial locations. For example, object X was rewarded if it was on the left but not if it was on the right. After ablation of part of the dorsal prestriate cortex they were impaired in learning discriminations of this kind. The same animals were not impaired in learning visual object discriminations in which spatial position was irrelevant, nor in learning spatial discriminations in which object identity was irrelevant. The results were compared with previously reported results from fornix transection in the same tasks; the deficit following dorsal prestriate ablation in visuospatial configural discrimination learning was similar in severity to that which followed fornix transection. The results show that the dorsal prestriate area has a more general role in visuospatial processing than was known hitherto, and they suggest that it interacts with the hippocampal formation and fornix in visuospatial memory tasks.     

Performance on spatial working memory tasks after dorsal or ventral hippocampal lesions and adjacent damage to the subiculum.

Rats with excitotoxic lesions of the dorsal or ventral hippocampus and control rats were trained on 2 spatial working memory tasks: the standard version of the radial maze with 8 baited arms and the nonmatching-to-place procedure in the T maze. Dorsal lesions produced deficits in both tasks, whereas ventral lesions did not affect learning in either of them. A volumetric analysis of subicular damage showed that dorsal hippocampal lesions caused a deficit in the nonmatching-to-place only when accompanied by damage to the dorsal subiculum; on the other hand, lesions to the dorsal hippocampus impaired performance in the radial-arm maze regardless of the extent of subicular damage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Reversal set formation in the visually decorticate rat.

Results of 4 experiments with 32 male black-hooded rats show that Ss given large visual cortex lesions demonstrated a simultaneous task reversal deficit previously reported by R. C. Gonzales et al (1964) to follow more extensive cortical ablation. However, no deficit appeared in an operant discrimination that deemphasized visuospatial cues, and the simultaneous task deficit vanished when translucent eye occluders were applied to eliminate spatial, but not intensity, cue use. Because the lesion Ss showed an impairment only when visuospatial cues were available and relevant to correct reversal performance, they seemed hindered by their incompetent processing of visuospatial information. Results support spatial rather than learning approaches to visual cortex function. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual size processing in spatial neglect

Evidence from the use of the landmark task and from two size-matching tasks shows that many patients with left-sided neglect systematically under-perceive visual extent in leftward parts of space. This perceptual distortion of size serves to explain the occurrence of rightward line-bisection errors in most neglect patients. One possibility is that attentional biases of a chronic nature might underlie these perceptual changes seen in neglect patients. But contrary to this idea, we have found that attentional cueing in the landmark task causes changes in neglect patients exactly opposite to those seen in healthy subjects. The distortions of size perception seen in neglect could instead be caused by a high-level alteration of visual processing rather than by an attentional bias. In order to explore which visual stream of cortical processing might be compromised in such a disorder, we have begun to examine neglect patients on visuomotor as well as perceptual tasks. We have found clear evidence in one patient for intact grip scaling for object size in the neglected half of space, despite gross perceptual underestimations of the same objects. This result suggests that neglect can occur without major disruption of the dorsal stream, and may result instead from damage to a cortical system whose predominant visual input comes from the ventral stream.     

Dissociating the roles of dorsal and ventral CA1 for the temporal processing of spatial locations, visual objects, and odors.

The differential contributions of the dorsal and ventral hippocampus for learning and memory have long been of interest. The present experiments were designed to evaluate the contributions of dorsal CA1 and ventral CA1 for temporal processing. Animals were run on three temporal ordering paradigms: one with visual objects, one with olfactory stimuli, and one with spatial locations. Animals with lesions to dorsal CA1 showed deficits for the temporal ordering of visual objects relative to control animals, and deficits for the temporal ordering of spatial locations relative to control and ventral CA1 lesioned animals. Animals with lesions to ventral CA1 showed deficits for the temporal ordering of olfactory information relative to control and dorsal CA1 lesioned animals, and a mild deficit for the temporal ordering of visual objects relative to control animals, but not as severe as those shown by the dorsal CA1 lesioned animals. These data suggest that dorsal CA1 and ventral CA1 contribute to temporal ordering processes, and that dorsal CA1 and ventral CA1 are dissociable for temporal ordering based upon the nature of the information that is processed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Differential involvement of the dorsal anterior cingulate and prelimbic-infralimbic areas of the rodent prefrontal cortex in spatial working memory": Correction to Ragozzino et al. (1998).

Reports an error in "Differential involvement of the dorsal anterior cingulate and prelimbic-infralimbic areas of the rodent prefrontal cortex in spatial working memory" by Michael E. Ragozzino, Spencer Adams and Raymond P. Kesner (Behavioral Neuroscience, 1998[Apr], Vol 112[2], 293-303). Figure 1 (page 295) and Figure 4 (page 299) were printed incorrectly. The corrected figure pages and corresponding captions are provided in the erratum. (The following abstract of the original article appeared in record 1998-01023-003.) The present study examined the effects of quinolinic acid lesions of the dorsal anterior cingulate and prelimbic-infralimbic cortices on spatial working memory and spatial discrimination using go/no-go procedures. All testing occurred in a 12-arm radial maze. In a working memory task, rats were allowed to enter 12 arms for a cereal reward. Three or 4 arms were presented for a 2nd time in a session, which did not result in a reward. In a spatial discrimination task, rats had successive access to 2 different arms. One arm always contained a reward, and the other never contained a reward. Prelimbic-infralimbic lesions impaired spatial working memory but only produced a transient spatial discrimination deficit. Dorsal anterior cingulate lesions did not induce a deficit in either task. These findings suggest that the prelimbic-infralimbic cortices, but not the anterior cingulate cortex, are important in spatial working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

When do additional distractors reduce the attentional blink?

When 2 targets are embedded in a rapid serial visual presentation stream of distractors, perception of the second target is impaired when the intertarget lag is relatively short (less than 500 ms). Stimuli concurrently presented with the stream can affect this phenomenon, which is called attentional blink (AB). Previous studies have yielded conflicting results concerning the direction of the effect of added distractors on the AB: Some studies report an increased AB, whereas others report a decreased AB. The present study explored the boundary conditions of the exaggeration–reduction effects of distractors on the AB and investigated underlying mechanisms by manipulating the spatial configuration, timing, and type of distractors. The results indicate that the magnitude of the AB deficit increased, regardless of the type of distractors, when spatial uncertainty of the target locations was involved. The reduction of the AB occurred at optimal presentation of distractors and disappeared when the second target was presented at a suprathreshold level. These results suggest that stochastic resonance or the center-surround attentional mechanism may contribute to the reduction effect of distractors on the AB deficit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of temperature and synaptic blockade in vitro on neurons of the horizontal limb of the diagonal band of Broca in the rat basal forebrain

We studied the thermosensitivity of neurons in the rat horizontal limb of the diagonal band of Broca (HDB) in vitro under normal conditions and under conditions of a low calcium/high magnesium synaptic blockade (SB). Of 52 HDB neurons tested, 34 neurons (65%) were warm-sensitive (WS), three neurons (6%) were cold-sensitive (CS), 11 neurons (21%) were temperature-insensitive (TI) and four additional neurons (8%) were both warm- and cold-sensitive (WS/CS). Of 34 neurons tested for thermosensitivity under SB, 11 were WS, 4 were CS and 19 were TI. Nearly half (48%) of the WS neurons maintained warm sensitivity under SB, 43% became TI and 9% became CS. Baseline firing rates of neurons significantly decreased during SB and then increased during recovery from SB. In addition, a distinct anatomical distribution of thermosensitive neurons was found in the HDB. The most ventral aspect of the HDB (interaural +0.9-1.3 mm) had proportionally fewer temperature sensitive neurons (65% vs. 88%) than areas more dorsal (interaural +1.3-1.7 mm), and only one of seven ventral HDB neurons (14%) remained thermosensitive during SB. In the dorsal HDB, 65% of the neurons maintained thermosensitivity during SB. These results demonstrate that the HDB contains inherently thermosensitive neurons, and that a difference in thermal characteristics exists between the ventral and dorsal HDB neurons.     

Morris water maze deficits in rats following traumatic brain injury: lateral controlled cortical impact

This experiment utilized a laterally placed controlled cortical impact model of traumatic brain injury (TBI) to assess changes on spatial learning and memory in the Morris water maze (MWM). Adult rats were subjected to one of two different levels of cortical injury, mild (1 mm) or moderate (2 mm) deformation, and subsequently tested for their ability to learn (acquisition) or remember (retention) a spatial task, 7 or 14 days after injury. Results revealed an injury-dependent deficit for experimental animals compared to sham-operated controls. Not only did the TBI result in longer escape latencies, but also significant deficits in search time and relative target visits. Although the moderately injured animals demonstrated significant histopathology in the cortex and hippocampus, mildly injured subjects demonstrated no obvious tissue destruction, but did manifest significant behavioral change. These results demonstrate that a laterally placed controlled cortical impact is capable of producing significant cognitive deficits on both acquisition and retention paradigms utilizing the MWM.     

Impaired orienting of attention in left unilateral neglect: A componential analysis.

Twenty-six patients suffering from damage to the right side of the brain, 19 of whom exhibited signs of left neglect, as well as 32 matched controls, ran 3 spatial cuing tasks. Patients were also tested with 2 cancellation tests, a line-bisection test, the copy of a complex drawing, and a visual extinction procedure. Results first showed correlations between extinction and cancellation tests performance on one hand, and between line bisection and copy on the other hand. Second, results demonstrated that an engagement deficit toward contralesional targets appeared to be the most striking feature of neglect, and the engagement score was correlated with the cancellation score and extinction. Most patients with neglect also presented a deficit in disengagement, a deficit of inhibition of return, and probably a deficit of alertness. Deficits in engagement and in disengagement, as well as poor scores in cancellation tests, seemed to be related with posterior cortical and subcortical lesions. Most important, even if an endogenous deficit (frequently related with a thalamic lesion) could aggravate the neglect behavior, neglect syndrome was mainly explained by a deficit of exogenous attention. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Response–reinforcer associations after caudate-putamen lesions in the rat: Spatial discrimination and overshadowing–potentiation effects in instrumental learning.

Exp I, with 12 male hooded rats, demonstrated that Ss with caudate-putamen lesions exhibited an impairment in the acquisition and reversal of a spatial maze task when compared with unoperated control Ss. Exp II, with 24 Ss, investigated leverpress responding supported by a VI schedule in 3 groups of Ss: a group with caudate-putamen lesions, a group with lesions of the posterior cortex, and an unoperated control group. The presentation of a 0.5-sec, response-contingent light correlated with reinforcement generated an elevated response rate in the 2 operated groups but tended to suppress responding in the control group, perhaps by overshadowing the response–reinforcer relation. Only the group with cortical lesions maintained the elevated rate when the light was uncorrelated with food delivery. Exp III confirmed for these same Ss that caudate-putamen lesions produced a spatial learning deficit. No deficit was observed in the posterior cortex group. It is suggested that caudate-putamen lesions disrupt the mechanism underlying the response–reinforcer association on which spatial maze learning and free operant responding in part depend. (48 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Linear changes in the spatial extent of the focus of attention across time.

This research examined changes in the spatial extent of focal attention over time. The Attentional Blink (impaired perception of the second of two targets) and Lag-1 sparing (the seemingly paradoxical finding that second-target accuracy is high when the second target immediately follows the first) were employed in a dual-stream paradigm to index spatiotemporal changes in focal attention. Lag-1 sparing occurs to targets in different streams if the second target falls within the focus of attention. Focal attention is assumed to initially encompass both streams but to shrink rapidly to the first-target stream, thus withdrawing from the second target if it appears in the opposite stream. The time available for the focus to shrink before second target onset was manipulated by varying the stimulus-onset asynchrony (SOA) between successive items in the stream. There was a progressive transition from Lag-1 sparing to its converse (Lag-1 deficit) as the SOA was increased. This transition was related linearly to SOA, which suggests that the spatial extent of focal attention varies linearly over time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential involvement of the dorsal anterior cingulate and prelimbic–infralimbic areas of the rodent prefrontal cortex in spatial working memory.

[Correction Notice: An erratum for this article was reported in Vol 112(4) of Behavioral Neuroscience (see record 2008-09590-001). Figure 1 (page 295) and Figure 4 (page 299) were printed incorrectly. The corrected figure pages and corresponding captions are provided in the erratum.] The present study examined the effects of quinolinic acid lesions of the dorsal anterior cingulate and prelimbic–infralimbic cortices on spatial working memory and spatial discrimination using go/no-go procedures. All testing occurred in a 12-arm radial maze. In a working memory task, rats were allowed to enter 12 arms for a cereal reward. Three or 4 arms were presented for a 2nd time in a session, which did not result in a reward. In a spatial discrimination task, rats had successive access to 2 different arms. One arm always contained a reward, and the other never contained a reward. Prelimbic–infralimbic lesions impaired spatial working memory but only produced a transient spatial discrimination deficit. Dorsal anterior cingulate lesions did not induce a deficit in either task. These findings suggest that the prelimbic–infralimbic cortices, but not the anterior cingulate cortex, are important in spatial working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Organization of the visual reticular thalamic nucleus of the rat

The visual sector of the reticular thalamic nucleus has come under some intense scrutiny over recent years, principally because of the key role that the nucleus plays in the processing of visual information. Despite this scrutiny, we know very little of how the connections between the reticular nucleus and the different areas of visual cortex and the different visual dorsal thalamic nuclei are organized. This study examines the patterns of reticular connections with the visual cortex and the dorsal thalamus in the rat, a species where the visual pathways have been well documented. Biotinylated dextran, an anterograde and retrograde tracer, was injected into different visual cortical areas [17; rostral 18a: presumed area AL: (anterolateral); caudal 18a: presumed area LM (lateromedial); rostral 18b: presumed area AM (anteromedial); caudal 18b: presumed area PM (posteromedial)] and into different visual dorsal thalamic nuclei (posterior thalamic, lateral geniculate nuclei), and the patterns of anterograde and retrograde labelling in the reticular nucleus were examined. From the cortical injections, we find that the visual sector of the reticular nucleus is divided into subsectors that each receive an input from a distinct visual cortical area, with little or no overlap. Further, the resulting pattern of cortical terminations in the reticular nucleus reflects largely the patterns of termination in the dorsal thalamus. That is, each cortical area projects to a largely distinct subsector of the reticular nucleus, as it does to a largely distinct dorsal thalamic nucleus. As with each of the visual cortical areas, each of the visual dorsal thalamic (lateral geniculate, lateral posterior, posterior thalamic) nuclei relate to a separate territory of the reticular nucleus, with little or no overlap. Each of these dorsal thalamic territories within the reticular nucleus receives inputs from one or more of the visual cortical areas. For instance, the region to the reticular nucleus that is labelled after an injection into the lateral geniculate nucleus encompasses the reticular regions which receive afferents from cortical areas 17, rostral 18b and caudal 18b. These results suggest that individual cortical areas may influence the activity of different dorsal thalamic nuclei through their reticular connections.