Neural correlates to both emotion and cognitive functions in the monkey amygdala

Recent lesion and non-invasive studies identify the medial temporal lobe, including the amygdala, not only with emotion but also with working memory in relation to the prefrontal cortex. In the present study, amygdalar neuronal activity was recorded from monkeys during performance of discrimination tasks that led to presentation of emotion-related (rewarding or aversive) stimuli. The task had three phases: (1) discrimination (visual, auditory), (2) operant response (bar pressing) and (3) ingestion (reward) or avoidance (aversion). These neurons were further analyzed by a short-term memory task, delayed pair comparison (DPC) using colored lamps. Of 585 amygdalar neurons, 107 responded primarily to single sensory stimulation (40 vision related, 26 audition related, 41 ingestion related), 117 to multimodal stimulation (multimodal) and 14 responded selectively to only one item (selective). Of 417 neurons tested by the DPC, 122 responded in one or more phases. Of these 122 neurons, 10.7% responded in the delay period. These delay-responsive neurons also responded to various objects with positive and negative affective significance. These results suggest that amygdalar neurons are not specifically related to working memory, as are those in the inferotemporal and prefrontal cortices, but are related to more general non-specific functions or processes such as arousal or attention during the cognitive tasks. A functional role of the amygdala in working memory is discussed in terms of recent non-invasive studies suggesting a functional coupling between the amygdala and prefrontal cortex.     

Neuronal responses in monkey lateral hypothalamus during operant feeding behavior

Single neuron activity was recorded from monkey lateral hypothalamus to investigate neuronal events correlated with operant bar press feeding behavior. The behavioral paradigm was divided into three phase: visual (discrimination), bar press (procurement), and ingestion (consummatory). Of 669 neurons tested, 158 (24%) responded in one or more phases. During the visual phase, 106 neurons (16%) responded. Of 80 neurons that responded in the visual phase and were tested systematically, 33 (41%, 33/80) responded selectively to the sight of food or nonfood objects associated with a juice reward, but not to the sight of nonfood or objects associated with aversive saline. Neuronal activity related to discrimination was modulated by satiation and learning (i.e., acquisition and extinction). During the bar press phase, 51 neurons (7.6%) responded. These responded tonically during the early or late stage of the bar press period, but did not depend on individual bar pressing motions. During ingestion, 90 neurons (13%) responded. The ingestion response was modulated by palatability of food and satiation. Data suggest that the LHA is deeply involved in operant feeding behavior; discrimination of food, drive to get food, and perception of reward, all of which are affected by learning and internal states such as hunger and satiety.     

Single neuron responses in amygdala of alert monkey during complex sensory stimulation with affective significance

Among other deficits, amygdalectomy impairs the ability of the animal to recognize the affective significance of a stimulus. In the present study, neuronal activity in the amygdala (AM) was recorded from alert monkeys while they performed tasks leading to the presentation of rewarding or aversive stimuli. Of 585 AM neurons tested, 312 (53.3%) responded to at least one stimulus in one or more of 5 major groups: 40 vision related, 26 audition related, 41 ingestion related, 117 multimodal, and 14 selective. Ingestion-related neurons were subdivided according to their responses to other stimuli: oral sensory, oral sensory plus vision, and oral sensory plus audition. Depending upon their responsiveness to the affective significance of the stimuli, neurons in the vision- and audition-related categories were divided into 2 subclasses: vis-I (26/40), vis-II (14/40), aud-I (8/26), and aud-II (18/26). All 4 subtypes usually responded to unfamiliar stimuli but seldom responded to neutral familiar stimuli. Types vis-I and aud-I responded to both positive and negative familiar stimuli. Types vis-II and aud-II responded to certain familiar negative stimuli but not to familiar positive stimuli. In vis-I neurons, responses were stronger for palatable foods than for less palatable foods. No neurons within vision-related, audition-related, and multimodal categories responded solely to positive or to negative stimuli. Of the 27 oral sensory neurons 9 were tested with saline or salted food, and 8 responded to normally aversive oral sensory stimuli in the same manner as they did to normal food or liquid (water or juice). In contrast to oral sensory neurons, all responses of 4 oral sensory-plus-vision and all of 4 selective neurons tested, as well as bar pressing behavior, were modulated by altering the affective significance of the food. These results suggest that the AM is one of the candidates for stimulus-affective association based on associative learning and memory.     

Single neuron activity in dorsolateral prefrontal cortex of monkey during operant behavior sustained by food reward

The activity of 190 neurons was recorded from the dorsolateral prefrontal cortex of monkeys during an operant task that consisted of 3 phases: visual discrimination of food and non-food, bar pressing to gain access to the food and ingestion. In area 8, a fairly large proportion of the 49 recorded neurons responded in both the visual discrimination (37%) and motor initiation (35%) phases. Some functional heterogeneity seems evident within area 8 since visual discrimination responses were rostral, visuokinesis was central and motor initiation was in the caudal bank of the arcuate sulcus. Neurons in area 9 responded primarily (37%) during the bar pressing phase and less during the visual discrimination phase. Neurons in area 10 responded variously during most phases of the task--food discrimination, bar pressing, and ingestion. Neurons in the periprincipal sulcal area usually responded in the visual discrimination phase, but some which did not respond to food presented in front of the subject responded to meaningful visual or auditory cues that were related to food reward. The data suggest that neurons in the dorsolateral prefrontal cortex have multiple functions related to all phases of complex, learned feeding behavior. Functional roles of the prefrontal cortex and the lateral hypothalamus in development of feeding behavior are discussed.     

Functional properties of dorsolateral prefrontal cortical neurons in awake monkey.

Electrophysiological single-cell responses were studied in 134 neurons in Walker's areas 46 and 9 of the prefrontal cortex of two stumptail macaques. The neurons were systematically tested for various visual, auditory and somatosensory stimuli. In addition, the rate of neuronal discharges were observed in relation to provoked or spontaneous eye or limb movements. More than half (52.2%) of the neurons responded to stimulation, and the majority of them gave visual responses. Eighty percent of the visual neurons responded to the presentation of various objects, the remaining being selective for meaningful objects or the appearance and movements of the experimenter. Auditory, somatosensory, somatomotor and oculomotor responses were also encountered; 9.0% of the recorded neurons were multimodal. Despite the large stimulus repertoire 47.8% of the neurons were found to be only spontaneously active.     

Neuron activity in and adjacent to the dorsal amygdala of monkey during operant feeding behavior

Neuronal activity of the dorsal amygdala, the substantia innominata and the ventral putamen during bar press operant behavior was analyzed to investigate neuronal responses in various affective situations. Of 1507 neurons recorded, 431 responded to some stimuli and were classified into 6 functional categories: 64 (4.2%) indiscriminately and transiently responded to various stimuli; 98 (6.5%) responded to various objects depending on their significance, whether rewarding or punishing; 44 (2.9%) clearly responded only to certain food or objects associated with potables, but not to both; 16 (1.1%) responded to both food and objects associated with potables; 35 (2.3%) responded primarily at the sight of certain nonfood; 66 (4.4%) responded primarily in the ingestion phase. Relations between function and topography are discussed. The results suggest that the dorsal AM and adjacent areas might be important in recognizing the biological significance of objects and in procuring food.     

Single unit activity during a Go/NoGo task in the "prefrontal cortex" of pigeons.

Single unit activity was recorded during a delayed auditory/visual Go/NoGo task from the neostriatum caudolaterale (NCL) of pigeons, a multimodal associative avian forebrain structure comparable to the prefrontal cortex (PFC). The animals were trained to mandibulate (to open their beak) during the Go period after which they received a drop of water as reward. Neuronal activity changes were observed during the delay period (DELAY) between auditory and visual stimulation, to the onset of the visual stimulus or to the delivery of the reward. In some neurons, responses were related to the behavioral significance of the stimulus such that the neuronal activity was statistically different between Go and NoGo trials. Moreover, some units anticipated the upcoming reward or changed their firing frequency in a correlated manner prior to beak movements. These neuronal activity patterns suggest that the NCL provides a neural network that participates in the integration and processing of external stimuli in order to generate goal directed behavior.     

Single unit activity during a Go/NoGo task in the “prefrontal cortex” of pigeons

Single unit activity was recorded during a delayed auditory/visual Go/NoGo task from the neostriatum caudolaterale (NCL) of pigeons, a multimodal associative avian forebrain structure comparable to the prefrontal cortex (PFC). The animals were trained to mandibulate (to open their beak) during the Go period after which they received a drop of water as reward. Neuronal activity changes were observed during the delay period (DELAY) between auditory and visual stimulation, to the onset of the visual stimulus or to the delivery of the reward. In some neurons, responses were related to the behavioral significance of the stimulus such that the neuronal activity was statistically different between Go and NoGo trials. Moreover, some units anticipated the upcoming reward or changed their firing frequency in a correlated manner prior to beak movements. These neuronal activity patterns suggest that the NCL provides a neural network that participates in the integration and processing of external stimuli in order to generate goal directed behavior.     

Visual responses related to food discrimination in monkey lateral hypothalamus during operant feeding behavior

Single neuron activity was recorded from monkey lateral hypothalamic area (LHA) to relate neuronal events to food discrimination and initiation of procurement movement in operant bar press feeding behavior. Of 429 neurons tested, 68 (16%) responded during visual phase. Of these, 30 (7%) responded selectively to the sight of food or non-food associated with a juice reward, but not to the sight of meaningless non-food or food associated with aversive saline. Neuronal activity related to discrimination was readily influenced by extinction, reversal or satiation. The strength of visual responses was correlated with latency of bar press initiation and speed of bar pressing, but was not related directly to bar press movement. These suggest that the LHA is deeply involved in discrimination of reinforcement or non-reinforcement, and might be associated with higher functions to regulate internal states such as physiological need to get food during operant feeding behavior.     

Interaction of sound and sight during action perception: Evidence for shared modality-dependent action representations

Seeing or hearing manual actions activates the mirror neuron system, i.e., specialized neurons within motor areas which fire not only when an action is performed but also when it is passively perceived. Although it has been shown that mirror neurons respond to either action-specific vision or sound, it remains a topic of debate whether and how vision and sound interact during action perception.Here we used transcranial magnetic stimulation to explore multimodal interactions in the human motor system, namely at the level of the primary motor cortex (M1). Corticomotor excitability in M1 was measured while subjects perceived unimodal visual (V), unimodal auditory (A), or multimodal (V + A) stimuli of a simple hand action. In addition, incongruent multimodal stimuli were included, in which incongruent vision or sound was presented simultaneously with the auditory or visual action stimulus. A selective response increase was observed to the congruent multimodal stimulus as compared to the unimodal and incongruent multimodal stimuli.These findings speak in favour of ‘shared’ action representations in the human motor system that are evoked in a ‘modality-dependent’ way, i.e., they are elicited most robustly by the simultaneous presentation of congruent auditory and visual stimuli. Multimodality in the perception of hand movements bears functional similarities to speech perception, suggesting that multimodal convergence is a generic feature of the mirror system which applies to action perception in general.     

Functional role of the limbic system and basal ganglia in motivated behaviors

It has been suggested that the cortico- and limbic-striatal systems are important in various motor functions such as motivated behaviors. In this paper we review our previous studies to investigate neuronal mechanisms of feeding behaviors. We recorded neuronal activity from the amygdala, caudate nucleus, globus pallidus, and substantia nigra during feeding behavior in monkeys, and compared neuronal responses recorded from these brain areas. First, of 710 amygdalar neurons tested, 129 (18.2%) responded to single sensory stimulation (48 to vision, 32 to audition, 49 to ingestion), 142 (20%) to multimodal stimulation, and 20 to only one item with affective significance. Eight food related amygdalar neurons were tested in reversal by salting food or introducing saline, and all responses were modulated by reversal. These results suggest that the amygdala might be important in ongoing recognition of the affective significance of complex stimuli (food-nonfood discrimination).

Second, activity was recorded from 351 neurons in the head of the caudate nucleus of monkeys during an operant feeding task. The 16% of these neurons responded in the discrimination phase. Some of these neurons responded specifically to food. The magnitude of these food-specific neurons depend on the rewarding nature of the food (reward value), and was inversely related to the latency of the onset of bar press. Of the caudate neurons, 10% responded in the bar press phase. Activity of most neurons which responded in the bar press phase was not correlated to individual bar presses. Cooling of the dorsolateral prefrontal cortex abolished sustained responses during bar pressing, but did not abolish the feeding behavior. However, bar press speed tended to be delayed by prefrontal cooling.

Third, activity of 358 neurons was recorded from the monkey globus pallidus, and 204 neurons responded during the feeding task. In the globus pallidus, few neurons responded to food in the discrimination phase. On the other hand, activity of most responsive neurons changed during bar press and/or ingestion phases. Activity of about half of these responsive neurons was directly related to specific feeding motor acts such as arm extension, flexion, bar pressing, grasping, chewing, etc. Some of these neurons showed motor-related responses with gradual and preparatory responses. These motor-related neurons were located mainly in the caudodorsal part of the globus pallidus. On the other hand, about one third, especially in the rostroventral part of the globus pallidus, showed dissociating responses in that they responded during bar pressing for food or during ingestion in an operant task, but not during bar pressing for nonfood or during forcible ingestion. The response magnitude of the neurons during arm extension and bar pressing depended on the nature of the food.

Fourth, activity of 261 neurons was recorded from the substantia nigra pars reticulata. Most of responding neurons (more than two-thirds of the recorded neurons) responded during the bar press and/or ingestion phases. Activity of the one-third of neurons was related to specific motor execution such as arm extension, flexion and bar pressing, but not to motor preparation. These neurons were located mainly in the rostral part of the nucleus. More than one-third of the recorded neurons responded during feed and/or drinking acts and intra- and perioral sensory stimuli, and were located mainly in the caudomedial part of the nucleus.

Based upon these responses and known anatomical evidence, various information including that from the amygdala and prefrontal cortex is integrated in the basal ganglia, and converted to coordinated motivated behaviors such as feeding behavior.

     

Motivation-related neuronal activity in the object discrimination task in monkey septal nuclei

Septal nuclei are suggested to work as an interface between the hippocampal formation, involved in higher cognitive functions, and the hypothalamus, involved in motivational behaviors such as feeding, drinking, and intracranial self-stimulation. In the present study, to elucidate a role of the septal nuclei in motivational behaviors, single neuron activity was recorded from water- and food-deprived monkeys during discrimination of objects associated with juice, and during ingestion of juice. Of 349 neurons recorded from two monkeys, 67 responded in the ingestion phase of the object discrimination task. Of these 67 neurons, 31 were further tested with the noncontingent liquid (juice or water) test in which liquid was provided until the animals became satiated. These 31 septal neurons were classified into two groups: type I neurons (n = 10) responded to juice ingestion with inhibition, and type II neurons (n = 21) responded with excitation. The spontaneous firing rates of the type I neurons were higher in the deprived condition and decreased as the animal became satiated by intake of liquid. Nine type II neurons responded to the sight of a white object associated with juice as well as ingestion of juice. The response magnitudes of the type II neurons to both the sight of the white object and ingestion of juice also decreased by satiation. However, spontaneous firing rates of the type II neurons did not change. These activity changes of both type I and II neurons were well correlated with changes in motivational state of the monkey estimated by the behavioral test. The results suggest that the activity of type I neurons reflects thirst or hunger drive levels, and that responses of type II neurons are related to reward perception. These type I and II neurons were located mainly in the anterior part of the septal nuclei. Results of the present study suggest, along with previous lesion and anatomical studies, that the septal nuclei exert a powerful influence on the motivational/drive systems through the projection to the hypothalamus. Hippocampus 1997;7:536–548. © 1997 Wiley-Liss, Inc.     

Neuronal responses of the rat amygdala during extinction and reassociation learning in elementary and configural associative tasks

To investigate functional heterogeneity within the amygdala in appetitive conditioned instrumental behaviours, neuronal activity was recorded from the amygdala of behaving rats during learning and discrimination of conditioned sensory stimuli associated with or without reinforcement [sucrose solution, intracranial self-stimulation (ICSS)]. Sensory stimuli included auditory (tone), visual (light) and configural (simultaneous presentation of tone and light) stimuli. The rat was trained to lick a spout protruded close to its mouth just after a conditioned sensory stimulus to obtain a reward. Of the 609 neurons recorded from the amygdala and amygdalostriatal transition area, 154 responded to one or more sensory stimuli. The 62 amygdalar neurons responded strongly to certain conditioned sensory stimuli associated with rewards. Of these 62 neurons, 45 were tested with the extinction trials. Responses of 31 neurons to conditioned stimuli were finally extinguished, and those of the remaining 14 were not extinguished. Furthermore, responses of 26 of these 31 neurons resumed in the relearning trials (plastic neurons), suggesting that these sensory responses were associative rather than just responses to physical properties of the stimuli. These plastic neurons were located mainly in the basolateral nucleus of the amygdala, and responses of the plastic neurons were correlated with behavioural responses. These results suggest that the basolateral nucleus is crucial in associative learning between sensory information and affective significance for behavioural outputs in appetitive conditioned instrumental behaviours.     

Spatial responsiveness of monkey hippocampal neurons to various visual and auditory stimuli.

To investigate involvement of the hippocampal formation in spatial information processing, activity of neurons in the hippocampal formation of the conscious monkey was recorded during presentation of various visual and auditory stimuli from several directions around the monkey. Of 1,047 neurons recorded, 106 (10.1%) responded to some stimuli from one or more directions. Of these 106 neurons with directionally differentiating responsiveness, 49 responded to visual stimulation, 35 to auditory stimulation, and 22 to both. Among 81 neurons, each tested with more than 10 different stimuli, one type responded independent of the nature of the stimulus (nonselective, n = 39), and responses of the other type depended on the nature of the stimulus (selective, n = 42). To investigate effects of change in spatial relations between test stimuli and background stimuli fixed on the monkey or fixed in the environment, 59 of 106 neurons were tested while the experimental apparatus holding the stimulus was moved relative to the monkey. Of these 59 neurons, 36 changed their responsiveness; 7 maintained the magnitude of their responses but changed the response direction with the movement of the apparatus, 5 changed direction regardless of the movement, and 24 did not change direction, but decreased or extinguished responses from the preferred direction. Thirty-two of 106 neurons were also tested by rotating the monkey. The directionally differentiating responsiveness of 11 neurons followed the monkey (egocentric neurons), that of 9 remained in place in the environment (allocentric neurons), and responses of 12 were reversibly extinguished when the monkey was rotated. The results suggest that these hippocampal neurons may be involved in identification of relations among various kinds of stimuli in different spatial frameworks (egocentric or allocentric) and this identification may be developed from multiple sensory modalities.     

Sensory response of cortical neurons in the anterior ectosylvian sulcus, including the area evoking eye movement.

The deep cortical tissue in the caudal portion of the anterior ectosylvian sulcus (AES) of cats anesthetized with alpha-chloralose was explored to examine the sensory response properties of neurons in this area, which is known to contain an area evoking eye movement. Of 873 neurons isolated, 262 (30.0%) were multimodal, i.e. responsive to two or more of the stimulus modalities of visual, auditory, or somatic. The ratio of multimodal neurons to total neurons in the eye-movement-evoking area was significantly larger than this ratio in other areas; 79 (39.5%) of 200 neurons in the eye-movement-evoking area were multimodal, while 183 (27.2%) of 673 neurons in other areas were multimodal. Neuronal minimal latency in response to visual stimulation was widely and bimodally distributed, showing two peaks at 35 ms and 60 ms, whereas latencies to auditory and somatic stimulation were narrowly distributed, with one peak at 10 ms and 15 ms, respectively. There was no remarkable difference either between unimodal neurons and multimodal neurons or between the neurons in the eye-movement-evoking area and those in other areas in distribution of latency. That there was a significant difference in ratio of multimodal to total neurons between the eye movement area and other areas suggests that some convergence or integration of different kinds of sensory input in relation to eye movement might be carried out in the caudal portion of the AES.     

Functional subdivisions of the temporal lobe neocortex

In order to gather evidence on functional subdivisions of the temporal lobe neocortex of the primate, the activity of more than 2600 single neurons was recorded in 10 myelo- and cytoarchitecturally defined subdivisions of the cortex in the superior temporal sulcus (STS) and inferior temporal gyrus of the anterior part of the temporal lobe of 5 hemispheres of 3 macaque monkeys. First, convergence of different modalities into each area was investigated. Areas TS and TAa, in the upper part of this region, were found to receive visual as well as auditory inputs. Areas TPO, PGa, and IPa, in the depths of the STS, received visual, auditory, and somatosensory inputs. Areas TEa, TEm, TE3, TE2, and TE1, which extend from the ventral bank of the STS through the inferior temporal gyrus, were primarily unimodal visual areas. Second, of the cells with visual responses, it was found that some neurons in areas TS-IPa could be activated only by moving visual stimuli, whereas the great majority of neurons in areas TEa-TE1 could be activated by stationary visual stimuli. Third, it was found that there were few sharply discriminating visual neurons in areas TS and TAa; of the sharply discriminating visual neurons in other areas, however, neurons that responded primarily to faces were found predominantly in areas TPO, TEa, and TEm (in which they represented 20% of the neurons with visual responses); neurons that were tuned to relatively simple visual stimuli such as sine-wave gratings, color, or simple shapes were relatively common in areas TEa, TEm, and TE3; and neurons that responded only to complex visual stimuli were common in areas IPa, TEa, TEm, and TE3. These findings show inter alia that areas TPO, PGa, and IPa are multimodal, that the inferior temporal gyrus areas are primarily unimodal, that there are areas in the cortex in the anterior and dorsal part of the STS that are specialized for the analysis of moving visual stimuli, that neurons responsive primarily to faces are found predominantly in areas TPO, TEa, and TEm, and that architectural subdivisions of the temporal lobe cortex are related to neuronal response properties.     

Auditory motion does not modulate spiking activity in the middle temporal and medial superior temporal visual areas

The integration of multiple sensory modalities is a key aspect of brain function, allowing animals to take advantage of concurrent sources of information to make more accurate perceptual judgments. For many years, multisensory integration in the cerebral cortex was deemed to occur only in high‐level “polysensory” association areas. However, more recent studies have suggested that cross‐modal stimulation can also influence neural activity in areas traditionally considered to be unimodal. In particular, several human neuroimaging studies have reported that extrastriate areas involved in visual motion perception are also activated by auditory motion, and may integrate audiovisual motion cues. However, the exact nature and extent of the effects of auditory motion on the visual cortex have not been studied at the single neuron level. We recorded the spiking activity of neurons in the middle temporal (MT) and medial superior temporal (MST) areas of anesthetized marmoset monkeys upon presentation of unimodal stimuli (moving auditory or visual patterns), as well as bimodal stimuli (concurrent audiovisual motion). Despite robust, direction selective responses to visual motion, none of the sampled neurons responded to auditory motion stimuli. Moreover, concurrent moving auditory stimuli had no significant effect on the ability of single MT and MST neurons, or populations of simultaneously recorded neurons, to discriminate the direction of motion of visual stimuli (moving random dot patterns with varying levels of motion noise). Our findings do not support the hypothesis that direct interactions between MT, MST and areas low in the hierarchy of auditory areas underlie audiovisual motion integration.     

Hippocampus and medial temporal cortex: neuronal activity related to behavioural responses during the performance of memory tasks by primates

Neuronal activity was recorded in the hippocampal formation, the parahippocampal gyrus and medial inferotemporal cortex of monkeys performing memory tasks. In a modified delayed matching to sample task in which 2 sequentially presented stimuli were compared on each trial, a match condition required a right panel press, whereas a non-match condition required a left panel press. The activity of 336/736 (45.7%) neurons was related to the behavioural responses (left or right panel presses) in this task. The incidence of response-related activity was 57.4% in cortical areas adjacent to the rhinal sulcus plus medial inferotemporal cortex, and 40.2% for the hippocampal formation. For 58.9% of these response-related neurons, the activity change associated with the behavioural response was greater than that during presentation of the sensory stimuli, though neurons commonly responded (33.2% of all recorded neurons) to both sensory and motor events. The activity of 198 neurons (26.9%) differed between go-left and go-right trials; such neurons were found in all areas but were nearly twice as common in the posterior as in the anterior hippocampal formation. The importance of visual stimuli for the response-related neuronal activity was examined during the performance of a delayed alternation task without visual cues indicating direction of response. The response-related activity of 8 neurons recorded during the delayed alternation and the delayed matching tasks was similar in both tasks, indicating that memory for the behavioural responses influences the activity of the response-related neurons. In order to test the effects of stimulus familiarity and non-spatial responses on medial temporal neurons, recognition memory and visual discrimination tasks requiring lick responses were performed. The activity of 2/375 (0.5%) neurons was related to the lick responses; 3/68 neurons in the inferomedial temporal cortex responded on the basis of stimulus novelty and none reflected their reinforcement value. It is concluded that the hippocampal formation, the parahippocampal gyrus and medial inferotemporal cortex all have a role in the utilisation of sensory, mnemonic and motor information underlying the selection of spatially-directed behavioural responses.     

Characterization of oculomotor and visual activities in the primate pedunculopontine tegmental nucleus during visually guided saccade tasks

The pedunculopontine tegmental nucleus (PPTN) has anatomical connections with numerous visuomotor areas including the basal ganglia, thalamus, superior colliculus and frontal eye field. Although many anatomical and physiological studies suggest a role for the PPTN in the control of conditioned behavior and associative learning, the detailed characteristics of saccade‐ and visual‐related activities of PPTN neurons remain unclear. We recorded the activity of PPTN neurons in monkeys (Macaca fuscata ) during visually guided saccade tasks, and examined the response properties of saccade‐ and visual‐related activities such as time course, direction selectivity and contextual modulation. Saccade‐related activity occurred either during saccade execution or after saccade end. The preferred directions of the neuronal activity were biased toward the contralateral and upward sides. Half of the saccade‐related neurons showed activity modulation only for task saccades and not for spontaneous saccades outside the task. Visually‐responsive neurons responded with short latencies. Some responded to the appearance of the visual stimulus in a directionally selective manner, and others responded to both the appearance and disappearance of the visual stimulus in a directionally non‐selective manner. Many of these neurons exhibited distinct visual responses to the appearance of two different stimuli presented under different stages of the task, whereas a population of the neurons responded equally to the disappearance of the two stimuli. Thus, many PPTN neurons exhibited context‐dependent activity related to the visuomotor events, consistent with a role in controlling conditioned behavior.     

Fos imaging reveals differential neuronal activation of areas of rat temporal cortex by novel and familiar sounds

To provide information about the possible regions involved in auditory recognition memory, this study employed an imaging technique that has proved valuable in the study of visual recognition memory. The technique was used to image populations of neurons that are differentially activated by novel and familiar auditory stimuli, thereby paralleling previous studies of visual familiarity discrimination. Differences evoked by novel and familiar sounds in the activation of neurons were measured in different parts of the rat auditory pathway by immunohistochemistry for the protein product (Fos) of the immediate early gene c-fos. Significantly higher counts of stained neuronal nuclei (266 +/- 21/mm2) were evoked by novel than by familiar sounds (192 +/- 17/mm2) in the auditory association cortex (area Te3; AudA). No such significant differences were found for the inferior colliculus, primary auditory cortex, postrhinal cortex, perirhinal cortex (PRH), entorhinal cortex, amygdala or hippocampus. These findings are discussed in relation to the results of lesion studies and what is known of areas involved in familiarity discrimination for visual stimuli. Differential activation is produced by novel and familiar individual stimuli in sensory association cortex for both auditory and visual stimuli, whereas the PRH is differentially activated by visual but not auditory stimuli. It is suggested that this latter difference is related to the nature of the particular auditory and visual stimuli used.