Corticostriatal and corticotectal projections from visual cortical areas 17, 18 and 18a in the pigmented rat

Striatum supports fast learning but not memory recall

Animals learn to carry out motor actions in specific sensory contexts to achieve goals. The striatum has been implicated in producing sensory-motor associations, yet its contribution to memory formation or recall is not clear. To investigate the contribution of striatum to these processes, mice were taught to associate a cue, consisting of optogenetic activation of striatum-projecting neurons in visual cortex, with forelimb reaches to access food pellets. As necessary to direct learning, striatal neural activity encoded both the sensory context and outcome of reaching. With training, the rate of cued reaching increased, but brief optogenetic inhibition of striatal activity arrested learning and prevented trial-to-trial improvements in performance. However, the same manipulation did not affect performance improvements already consolidated into short- (within an hour) or long-term (across days) memories. Hence, striatal activity is necessary for trial-to-trial improvements in task performance, leading to plasticity in other brain areas that mediate memory recall.

Learning speed and detection sensitivity controlled by distinct cortico-fugal neurons in visual cortex

Vertebrates can change their behavior upon detection of visual stimuli according to the outcome their actions produce. Such goal-directed behavior involves evolutionary conserved brain structures like the striatum and optic tectum, which receive ascending visual input from the periphery. In mammals, however, these structures also receive descending visual input from visual cortex (VC), via neurons that give rise to cortico-fugal projections. The function of cortico-fugal neurons in visually guided, goal-directed behavior remains unclear. Here, we address the impact of two populations of cortico-fugal neurons in mouse VC in the learning and performance of a visual detection task. We show that the ablation of striatal projecting neurons reduces learning speed, whereas the ablation of superior colliculus projecting neurons does not impact learning but reduces detection sensitivity. This functional dissociation between distinct cortico-fugal neurons in controlling learning speed and detection sensitivity suggests an adaptive contribution of cortico-fugal pathways even in simple goal-directed behavior.

Coding of self-motion-induced and self-independent visual motion in the rat dorsomedial striatum

Evolutionary development of vision has provided us with the capacity to detect moving objects. Concordant shifts of visual features suggest movements of the observer, whereas discordant changes are more likely to be indicating independently moving objects, such as predators or prey. Such distinction helps us to focus attention, adapt our behavior, and adjust our motor patterns to meet behavioral challenges. However, the neural basis of distinguishing self-induced and self-independent visual motions is not clarified in unrestrained animals yet. In this study, we investigated the presence and origin of motion-related visual information in the striatum of rats, a hub of action selection and procedural memory. We found that while almost half of the neurons in the dorsomedial striatum are sensitive to visual motion congruent with locomotion (and that many of them also code for spatial location), only a small subset of them are composed of fast-firing interneurons that could also perceive self-independent visual stimuli. These latter cells receive their visual input at least partially from the secondary visual cortex (V2). This differential visual sensitivity may be an important support in adjusting behavior to salient environmental events. It emphasizes the importance of investigating visual motion perception in unrestrained animals.

Multisensory integration in the mouse striatum

The basal ganglia are involved in sensorimotor functions and action selection, both of which require the integration of sensory information. In order to determine how such sensory inputs are integrated, we obtained whole-cell recordings in mouse dorsal striatum during presentation of tactile and visual stimuli. All recorded neurons responded to bilateral whisker stimulation, and a subpopulation also responded to visual stimulation. Neurons responding to both visual and tactile stimuli were located in dorsomedial striatum, whereas those responding only to whisker deflections were located dorsolaterally. Responses were mediated by overlapping excitation and inhibition, with excitation onset preceding that of inhibition by several milliseconds. Responses differed according to the type of neuron, with direct pathway MSNs having larger responses and longer latencies between ipsilateral and contralateral responses than indirect pathway MSNs. Our results suggest that striatum acts as a sensory “hub” with specialized functional roles for the different neuron types.

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Sensory integration in mouse striatum was studied using whole-cell in vivo recordings

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Neurons in dorsomedial striatum integrate tactile and visual sensory inputs

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Sensory responses are mediated by overlapping excitation and inhibition

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Bilateral sensory input is integrated differently by direct and indirect pathway MSNs

Contextual behavior and neural circuits

Animals including humans engage in goal-directed behavior flexibly in response to items and their background, which is called contextual behavior in this review. Although the concept of context has long been studied, there are differences among researchers in defining and experimenting with the concept. The current review aims to provide a categorical framework within which not only the neural mechanisms of contextual information processing but also the contextual behavior can be studied in more concrete ways. For this purpose, we categorize contextual behavior into three subcategories as follows by considering the types of interactions among context, item, and response: contextual response selection, contextual item selection, and contextual item–response selection. Contextual response selection refers to the animal emitting different types of responses to the same item depending on the context in the background. Contextual item selection occurs when there are multiple items that need to be chosen in a contextual manner. Finally, when multiple items and multiple contexts are involved, contextual item–response selection takes place whereby the animal either chooses an item or inhibits such a response depending on item–context paired association. The literature suggests that the rhinal cortical regions and the hippocampal formation play key roles in mnemonically categorizing and recognizing contextual representations and the associated items. In addition, it appears that the fronto-striatal cortical loops in connection with the contextual information-processing areas critically control the flexible deployment of adaptive action sets and motor responses for maximizing goals. We suggest that contextual information processing should be investigated in experimental settings where contextual stimuli and resulting behaviors are clearly defined and measurable, considering the dynamic top-down and bottom-up interactions among the neural systems for contextual behavior.

The non-lemniscal auditory cortex in ferrets: convergence of corticotectal inputs in the superior colliculus

Descending cortical inputs to the superior colliculus (SC) contribute to the unisensory response properties of the neurons found there and are critical for multisensory integration. However, little is known about the relative contribution of different auditory cortical areas to this projection or the distribution of their terminals in the SC. We characterized this projection in the ferret by injecting tracers in the SC and auditory cortex. Large pyramidal neurons were labeled in layer V of different parts of the ectosylvian gyrus after tracer injections in the SC. Those cells were most numerous in the anterior ectosylvian gyrus (AEG), and particularly in the anterior ventral field, which receives both auditory and visual inputs. Labeling was also found in the posterior ectosylvian gyrus (PEG), predominantly in the tonotopically organized posterior suprasylvian field. Profuse anterograde labeling was present in the SC following tracer injections at the site of acoustically responsive neurons in the AEG or PEG, with terminal fields being both more prominent and clustered for inputs originating from the AEG. Terminals from both cortical areas were located throughout the intermediate and deep layers, but were most concentrated in the posterior half of the SC, where peripheral stimulus locations are represented. No inputs were identified from primary auditory cortical areas, although some labeling was found in the surrounding sulci. Our findings suggest that higher level auditory cortical areas, including those involved in multisensory processing, may modulate SC function via their projections into its deeper layers.

Short-latency activation of striatal spiny neurons via subcortical visual pathways

The striatum is a site of integration of neural pathways involved in reinforcement learning. Traditionally, inputs from cerebral cortex are thought to be reinforced by dopaminergic afferents signaling the occurrence of biologically salient sensory events. Here, we detail an alternative route for short-latency sensory-evoked input to the striatum requiring neither dopamine nor the cortex. Using intracellular recording techniques, we measured subthreshold inputs to spiny projection neurons (SPNs) in urethane-anesthetized rats. Contralateral whole-field light flashes evoked weak membrane potential responses in approximately two-thirds of neurons. However, after local disinhibitory injections of the GABA(A) antagonist bicuculline into the deep layers of the superior colliculus (SC), but not the overlying visual cortex, strong, light-evoked, depolarizations to the up state emerged at short latency (115 +/- 14 ms) in all neurons tested. Dopamine depletion using alpha-methyl-para-tyrosine had no detectable effect on striatal visual responses during SC disinhibition. In contrast, local inhibitory injections of GABA agonists, muscimol and baclofen, into the parafascicular nucleus of the thalamus blocked the early, visual-evoked up-state transitions in SPNs. Comparable muscimol-induced inhibition of the visual cortex failed to suppress the visual responsiveness of SPNs induced by SC disinhibition. Together, these results suggest that short-latency, preattentive visual input can reach the striatum not only via the tecto-nigro-striatal route but also through tecto-thalamo-striatal projections. Thus, after the onset of a biologically significant visual event, closely timed short-latency thalamostriatal (glutamate) and nigrostriatal (dopamine) inputs are likely to converge on striatal SPNs, providing depolarizing and neuromodulator signals necessary for synaptic plasticity mechanisms.

The development of vision

Disorders of visual function are common findings in children with neonatal brain lesions of antenatal and perinatal onset. In the last few years the development of age appropriate batteries for assessing visual function in the first years and the combined use of neuroimaging and neurophysiological techniques have allowed to achieve better understanding of the mechanisms underlying development of vision in low risk infants and in those with brain lesions. We will review the main models of visual development and the tests available to assess visual function in infancy, focusing on the recently described battery of tests for assessing early visual abilities in preterm and full term infants.

Thalamic atrophy in infants with PVL and cerebral visual impairment

The aim of this retrospective study was to establish the presence and severity of cerebral visual impairment in preterm infants with PVL. We also wished to establish whether abnormalities of visual function are related to brain MRI findings and more specifically not only to the involvement of optic radiations and occipital cortex but also to changes in the thalami, that are often affected in infants with PVL. Twelve infants with cystic PVL were assessed at 1 year (+2) corrected age with a battery of tests specifically designed to assess various aspects of visual function in infancy, such as ocular movements, visual acuity, visual fields and fixation shift. All infants also had a brain MRI. Eleven of the 12 had involvement of the optic radiations: all had some abnormalities of visual function and visual impairment was more severe in infants with more extensive involvement of the optic radiations. The child with normal optic radiations had normal visual function. Six of the 12 infants also had obvious signs of atrophy of the thalami and all had severe and wide-ranging abnormalities of visual function in all testing domains. Two children had equivocal atrophy of the thalami, both had some abnormalities of visual function. Four children had normal thalami and had normal visual function or only minor abnormalities on one of the visual tests. Our results suggest that the atrophy of the thalami may play an additional role in the abnormal development of visual function in infants with PVL and abnormal optic radiations.

Definition and novel connections of the entopallium in the pigeon (Columba livia)

The avian entopallium (E) is the major thalamorecipient zone, within the telencephalon, of the tectofugal visual system. Because of discrepancies concerning the structure of this nuclear mass in pigeons, and in light of recent evidence concerning entopallial projections in other avian species, we here redefine and chart some novel entopallial projections in the pigeon by using a combination of cytochrome oxidase (CO) activity, calcium binding protein immunohistochemistry (CBPi), normal histology, and tract tracing. We show that 1) E is defined by the accurate overlap of CO activity and the dense terminations of thalamic (rotundal) efferents; 2) the perientopallium (Ep), E's overlying belt region, receives a relatively sparse rotundal input and is a major source of projections to wider regions of the hemisphere; and 3) E can be subdivided into internal (Ei) and external (Ex) portions on the basis of normal histology, CBPi, and differential projections. Thus, Ei, but not Ex, makes a reciprocal connection with a distinct nucleus in the ventrolateral mesopallium and is a major source of projections to the lateral striatum. These findings suggest the necessity for a revision of the original proposal of a strictly serial flow of visual information through the entopallial complex and further regions of the hemisphere and also require a modification of the long-standing view that E is comparable to only one specific lamina (IV) of extrastriate visual cortex of mammals. Rather, E appears to be composed of a variety of neuronal types possibly equivalent to those in several neocortical laminae.

Organization of electrically and chemically evoked defensive behaviors within the deeper collicular layers as compared to the periaqueductal gray matter of the rat

Stimulation of the periaqueductal gray matter (PAG) and the deeper layers of superior colliculus (SC) produces both freezing (tense immobility) and flight (trotting, galloping and jumping) behaviors along with exophthalmus (fully opened bulging eyes) and, less often, micturition and defecation. The topography of these behaviors within the distinct layers of SC remains unclear. Therefore, this study compared the defensive repertoire of intermediate (ILSC) and deep (DLSC) layers of SC to those of dorsolateral periaqueductal gray matter (DLPAG) and lateral periaqueductal gray matter (LPAG) [Neuroscience 125 (2004) 71]. Electrical stimulation was carried out through intensity- (0-70 microA) and frequency-varying (0-130 Hz) pulses. Chemical stimulation employed a slow microinfusion of N-methyl-d-aspartic acid (NMDA, 0-2.3 nmol, 0.5 nmol/min). Probability curves of intensity-, frequency- and NMDA-evoked behaviors, as well as the unbiased estimates of median stimuli, were obtained by threshold logistic analysis. Compared with the PAG, the most important differences were the lack of frequency-evoked jumping in both layers of SC and the lack of NMDA-evoked galloping in the ILSC. Moreover, although galloping and jumping were also elicited by NMDA stimulation of DLSC, effective doses were about three times higher than those of DLPAG, suggesting the spreading of the injectate to the latter structure. In contrast, exophthalmus, immobility and trotting were evoked throughout the tectum structures. However, whatever the response and kind of stimulus, the lowest thresholds were always found in the DLPAG and the highest ones in the ILSC. Besides, neither the appetitive, nor the offensive, muricide or male reproductive behaviors were produced by any kind of stimulus in the presence of appropriate targets. Accordingly, the present data suggest that the deeper layers of SC are most likely involved in the increased attentiveness (exophthalmus, immobility) or restlessness (trotting) behaviors that herald a full-blown flight reaction (galloping, jumping) mediated in the PAG.

Functional specializations within the tectum defense systems of the rat

Here we review the differential contribution of the periaqueductal gray matter (PAG) and superior colliculus (SC) to the generation of rat defensive behaviors. The results of studies involving sine-wave and rectangular pulse electrical stimulation and chemical (NMDA) stimulation are summarized. Stimulation of SC and PAG produced freezing and flight behaviors along with exophthalmus (fully opened bulged eyes), micturition and defecation. The columnar organization of the PAG was evident in the results obtained. Defecation was elicited primarily by lateral PAG stimulation, while the remaining defensive behaviors were similarly elicited by lateral and dorsolateral PAG stimulation, although with the lowest thresholds in the dorsolateral column. Conversely, the ventrolateral PAG did not appear to participate in unconditioned defensive behaviors, which were only elicited by high intensity stimulation likely to encroach on adjacent regions. In the SC, the most important differences relative to the PAG were the lack of stimulation-evoked jumping in both intermediate and deep layers, and of NMDA-evoked galloping in intermediate layers. Therefore, we conclude that the SC may be only involved in the increased attentiveness (exophthalmus, immobility) and restlessness (trotting) of prey species exposed to the cues of a nearby predator. These responses may be distinct from the full-blown flight reaction that is mediated by the dorsolateral and lateral PAG. However, other evidences suggest the possible influences of stimulation schedule, environment dimensions and rat strain in determining outcomes. Overall our results suggest a dynamically organized representation of defensive behaviors in the midbrain tectum.

Neurotoxic lesion of anteromedial/posterior parietal cortex disrupts spatial maze memory in blind rats

The primary visual cortex of rats is surrounded laterally (in Oc2L) and medially (in Oc2M) by several peristriate visual areas. Previous studies from our laboratory demonstrated that bilateral lesions in Oc2L result in visual pattern discrimination deficit, and in failure to solve a conditional discrimination which requires figure-background association. In contrast, neurotoxic lesions of the rostral part of Oc2M (which contains the anteromedial and anterior peristriate visual areas, collectively referred to as AM complex) result in deficits in visuospatial discrimination, and in disruptions in visual tasks involving spatial memory. The objective of this study was to behaviorally test the role of AM complex in a spatial memory task in absence of visual cues. For this purpose, we analyzed memory retention of Lashley III maze in blind rats after bilateral ibotenate lesions in AM complex, or in the primary visual cortex (V1, Oc1), to test the hypothesis that AM complex is essential for this cognitive task. The results showed a significant loss of memory retention of the maze in rats with lesions in AM complex, but not in rats with lesions in V1. Furthermore, the retention loss in rats with AM complex lesions was positively and significantly correlated with the size of the lesion. The results indicate a critical role of AM complex in spatial memory mechanisms independent on visual cues. A probable homology of rat AM complex with the posterior parietal cortex of primates is discussed.

Fetal cortical allografts project massively through the adult cortex

Allogeneic embryonic CNS tissue grafts placed in the mature brain are classically considered to lack significant long-range efferents. This problem was reexamined using 'green' cells from mice expressing ubiquitously an 'enhanced' green fluorescent protein as an alternative to classical tract tracing methods. The present study shows that fetal cortical neurons (E15; occipital origin) grafted in the occipitoparietal region of the adult cortex project massively throughout ipsilateral telencephalic structures. Two out of the nine grafted subjects had additional but sparse efferents in the visual thalamus, superior colliculus and pons.

Honeycomb-like structure of the intermediate layers of the rat superior colliculus: afferent and efferent connections

There is increasing evidence that acetylcholinesterase is organised in a lattice-like fashion in the intermediate layers of the mammalian superior colliculus. In a recent study, we described this organisation in rat by showing that it comprises a well formed honeycomb-like lattice with about 100 cylindrical compartments or modules occupying both the intermediate collicular layers. Considering this enzyme domain as a reference marker for comparing the organisation of collicular input-output systems, the present study investigates whether the principal sensori-motor systems in intermediate layers also have honeycomb-like arrangements. In 33 animals, the distributions of afferents (visual from extrastriate cortex; somatic from the primary somatosensory cortex, the trigeminal nucleus and the cervical spinal cord) and efferents (cells of origin of the crossed descending bulbospinal tract and uncrossed pathway to the pontine gray, the ascending system to the medial dorsal thalamus) were examined in a tangential plane following applications of horseradish peroxidase-wheatgerm agglutinin conjugate (used as an anterograde and retrograde tracer). In 22 of the 33 rats, axonal tracing was made within single tangential sections also stained for cholinesterasic activity in order to compare the neuron profiles with the cholinesterasic lattice.The results show that these afferent and efferent systems are also organised in honeycomb-like networks. Moreover, those related to the cortical, trigeminal and some of the spinal afferents are aligned with the cholinesterasic lattice. Likewise most of colliculo-pontine, colliculo-bulbospinal and half of colliculo-diencephalic projecting cells also tend to be in spatial register with the enzyme lattice. This indicates that the honeycomb-like arrangement is a basic architectural plan in the superior colliculus for the organisation of both acetylcholinesterase and major sensori-motor systems for orientation.

Corticostriatal activity in primary motor cortex of the macaque

Although input from corticostriatal neurons (CSNs) plays a critical role in basal ganglia functions, little is known about CSN activity during behavior. We compared the properties of antidromically identified CSNs with those of antidromically identified neurons that project via the cerebral peduncle to distant targets. Both types of neurons were recorded in primary motor cortex (M1) of two monkeys as they performed a step-tracking task in which static loads opposed or assisted simple and precued movements of the elbow or wrist. Multiple lines of evidence suggested that CSNs and corticopeduncular neurons (CPNs) belong to distinct populations. No cells were activated from both striatum and peduncle. Compared with CPNs, CSNs had slow conduction velocities and low spontaneous rates, and the activity of most was unmodulated by sensory testing or within the tasks used. CSN activity resembled that described for M1-recipient striatal neurons: perimovement firing was small in magnitude, strongly directional, and rarely showed muscle-like load effects. Contrary to a previous report, perimovement activity in most CSNs began before movement onset. CSN activity was more selective than that of CPNs: CSN sensory responses and perimovement activities were often directionally specific, CSNs were often activated exclusively by sensory stimulation, active movement, or movement preparation, and a substantial fraction of CSNs (19%) was unresponsive to any task or manipulation. Thus, CSNs transmit signals distinct from those sent to spinal cord/brainstem. The highly selective activity of CSNs suggests that a discrete (i.e., sparse) code is used to signal cortical activation states to striatum.

Lack of cortico-striatal projections from the primary auditory cortex in the squirrel monkey

The projections of the superior temporal gyrus to the caudate nucleus were studied in 10 squirrel monkeys (Saimiri sciureus). It was found that the primary auditory cortex lacks direct connections with the caudate nucleus as well as the putamen. Areas RL and T1 of Burton and Jones, bordering the primary auditory cortex laterally, show a moderate projection to the body and tail of the caudate nucleus; area T2, bordering areas RL and T1, shows an extensive projection into the head, body and tail. A comparison of the temporo-caudate projections of the monkey with those of rodents and carnivores suggests that primary and secondary auditory cortices differ in their connections in primates more than in other mammals, pointing to a greater functional differentiation of these areas in primates.

Basal ganglia damage and impaired visual function in the newborn infant

AIM

To examine the effects of early lesions in the visual pathway on visual function; and to identify early prognostic indicators of visual abnormalities.

METHODS

The visual function of 37 infants with perinatal brain lesions on magnetic resonance imaging was assessed using behavioural and electrophysiological variables.

RESULTS

Normal visual behaviour was observed in most infants with large bilateral occipital lesions, but all the infants with associated basal ganglia involvement had abnormal visual function. Visual abnormalities were also present in six infants with isolated basal ganglia lesions.

CONCLUSIONS

These observations suggest that basal ganglia may have an integral role in human visual development and that their presence on neonatal MRI could be an early marker of abnormal visual function.