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.     

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.

     

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.     

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.     

Role of monkey hippocampus in recognition of food and nonfood

To investigate the role of the hippocampal formation (HF) in feeding behavior, single neuron activity in the monkey HF was recorded during performance of an operant task that included food/nonfood discrimination, drinking, and active avoidance. Of 837 neurons recorded in the HF, 155 responded to the sight of one or more objects. Of these, 82 responded to the sight of different objects with different response magnitudes, and some of these 82 responded predominantly to food-related (rewarding) objects or nonfood, aversive objects. The magnitude of response of neurons that responded predominantly to food was not necessarily correlated with the order of animal's preference for those kinds of food. For some neurons that responded predominantly to food or nonfood, effects of extinction or reversal learning on the neuronal responses were tested, and most of the neurons tested maintained their original responsiveness even after behavioral extinction or reversal learning was accomplished. The results suggest that these HF neurons may be involved in preservation of past information concerning food or nonfood.     

Topographic distribution of modality-specific amygdalar neurons in alert monkey

Neuronal activity in the amygdala (AM) was recorded from alert monkeys during performance of tasks that led to presentation of rewarding or aversive stimuli. The tasks had 3 phases: (1) discrimination (visual, auditory), (2) operant response (bar pressing), and (3) ingestion (reward) or avoidance (aversion). Neuronal activity was analyzed and compared during each of these phases. Of 585 AM neurons tested, 312 (53.3%) responded to at least one stimulus in one or more of 5 major groups: vision related, audition related, ingestion related, multimodal, and selective. Forty neurons (6.8%) in the anterior dorsolateral capsule of the basolateral nuclei responded exclusively to visual stimuli (vision related). Twenty-six neurons (4.4%) further posterior in the basolateral group responded only to auditory stimuli (audition related). During ingestion an additional 41 neurons (7.0%) increased their activity (ingestion related). These were in the corticomedial group and at the boundaries between the nuclei of the basolateral group. Of these, 27 responded only in the ingestion phase, 11 during ingestion and at the sight of food, and 3 during ingestion and to certain sounds. Throughout the AM other neurons (n = 117, 20.0%) responded to visual, auditory, and somesthetic stimuli and, when tested, to involuntary ingestion of liquid (multimodal). Of these, 40 responded transiently (phasic; 36 excited, 4 inhibited). The remaining 77 maintained their altered activity into the subsequent phases of the task (tonic; 69 excited, 8 inhibited). In each of these 4 categories, most cells were activated primarily by novel or unfamiliar stimuli, and their responses habituated during repeated stimulation. A small number of cells in the basolateral and the basomedial nuclei (n = 14, 2.4%) were highly selective in that they responded specifically to one biologically significant object or sound more than to any other stimuli (selective). Some of these neurons responded to both sight and ingestion of a specific food. In summary, most AM neurons responded vigorously to novel stimuli, and some of the neurons had multimodal responsiveness. These results suggest the AM is related to processing of new environmental stimuli and to those cross-modal association.     

Neuronal responses in monkey anterior putamen during operant bar-press behavior

Single neuron activity was recorded in the monkey anterior putamen to compare visuomotor-related responses during operant bar-press behavior with visual discrimination of objects. Of 615 neurons recorded 9.8% ( ) responded to the presentation of food during forced delay of access to the bar. Of these 60 neurons, 38 were also tested with nonfood, and 19 of these responded to the nonfood objects regardless of the following movement. The amplitude of the visual-related responses of some differential neurons was graded for different objects to reflect the relative degree of preference for the food presented. However, these responses disappeared in reaction time tasks in which the bar could be accessed for pressing immediately upon presentation of an object. The visual response latency of differential neurons ranged from 50 to 700 ms (mean ± SD, 386 ±211 ms), which was longer than that of the nondifferential responses (207 ± 204 ms). These results suggest that anterior putamen neurons might participate in estimation of visual information that could be related to forecasting movement.     

Movement and non-movement related pallidal unit activity during bar press feeding behavior in the monkey

Activity was recorded from 358 neurons in the globus pallidus (GP) of monkeys (Macaca fuscata) during an operant feeding task consisting of 3 stages: (1) food or non-food presentation (1st stage); (2) bar pressing (2nd stage); and (3) food acquisition and ingestion (3rd stage). There were two kinds of neurons, one with high and the other with very low (almost silent), spontaneous firing rates. Two hundred and four neurons (57%) responded in one or more of the feeding stages. Of the 21 neurons which responded in the 1st stage, two responded selectively to food presentation, and 19 responded to both food and non-food visual presentation. One hundred and seventy-four neurons (49%) and 107 neurons (30%) responded in the 2nd and 3rd stages, respectively, and 106 (30%) of these were directly related to specific feeding motor acts such as arm extension, flexion, bar pressing, grasping, chewing etc. Both high and low firing neurons responded to motor acts with sharp or gradual onset. More than half of those that responded to arm extension showed laterality (contra or ipsi)- and function (extension or flexion)-dependent responses. The incidence of the motor related neurons was higher in the caudodorsal part of the GP. On the other hand, about one third, especially in the rostroventral part of the GP, 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 non-food or during forcible ingestion. The magnitude of firing changes during arm extension and bar pressing depended on the nature of the food. Moreover, in trials using new food or false (model) food, firing changes during bar press appeared or disappeared within a few trials with no correlation to bar press movement. These data suggest heterogeneous functions within the GP; the caudodorsal part is strictly concerned with motor execution and preparation, while the rostroventral part is not related to motor function directly, but may rather be important in coupling internal, motivational information to the motor system.     

Basal ganglia neural activity during operant feeding behavior in the monkey: relation to sensory integration and motor execution

The activity of single neurons in the caudate nucleus (CD), globus pallidus (GP), substantia nigra pars reticulata (SNr), and ventral tegmental area (VTA) was recorded during an operant feeding task in the monkey. The task had three phases: recognition of the food or nonfood stimulus (1st phase), bar pressing to obtain access to the stimulus (2nd phase), and ingestion (3rd phase). Data were collected from 351 neurons in CD, 344 in GP, 261 in SNr, and 275 in VTA. Neurons in the dorsolateral part of the CD, GP, and SNr responded primarily to motor events of feeding, i.e., extension/flexion of the arm, bar pressing, chewing, grasping or gazing. Neurons in the ventromedial part of the CD and rostroventral part of the GP exhibited differential responses to the presentation of food and nonfood during the recognition and bar pressing phases of the task. Neurons in the VTA increased their firing early in the bar pressing phase and then decreased their firing during ingestion. The data suggest that the dorsolateral part of the basal ganglia is involved mainly in motor function, while the ventromedial part may reflect the connection between motivation and motor output.     

Caudate unit activity during operant feeding behavior in monkeys and modulation by cooling prefrontal cortex

Activity was recorded from 351 neurons in the head of the caudate nucleus (CD) of monkeys during an operant feeding task consisting of: (1) food or non-food presentation (P); (2) bar pressing (B); and (3) food acquisition and ingestion (I). Of 45 neurons which responded in the P phase and were tested systematically, 27 responded to visual presentation of both food and non-food (non-specific response), and 18 responded to food presentation only (food specific response). The magnitude of food specific responses depended on the nature of the food and was inversely related to the latency of the onset of bar pressing. Thirty-five neurons responded in the B phase: 28 changed firing rate continuously with no correlation to individual bar presses, while the activity of the other 7 was related to each bar press. In the I phase, 62 neurons responded to separate events: the activity of more than half (39 neurons) was often related to chewing movement or gustatory stimuli, and that of one third (23 neurons) changed during individual arm movements. The neurons which responded in the P phase were found to be distributed widely in the head of the CD except for its central zone, while the neurons which responded in the I phase were in the medial part. Cooling of the dorsolateral prefrontal cortex abolished the continuous responses seen in the B phase, but did not abolish the feeding behavior. The data suggest that in the head of the CD there are several groups of neurons that have different functions and different distributions: food specific, sensory integration responses, non-motor responses driven by the frontal cortex, motor responses coupled to various movements, and sensory responses which apparently originate in the intra-oral cavity. These functions may arise sequentially, or in correspondence with integration of the sensory and motor systems to produce coordinated behavior.     

Neuronal activity in the ventral tegmental area (VTA) during motivated bar press feeding in the monkey

Neuronal activity of 58 dopaminergic (DA) and 200 non-dopaminergic (non-DA) neurons in the ventral tegmental area (VTA) of female monkeys was recorded, and correlation to bar press feeding, sensory stimulation and change in motivation was investigated. DA neurons, judged by duration of action potentials (more than 2.5 ms) and responsiveness to apomorphine, had lower firing rates (0-8 impulses/s); non-DA neurons had intermediate firing rates (10-30 impulses/s). Two-thirds of the DA and non-DA neurons responded in bar press feeding; the former with mostly tonic and the latter with phasic responses. Fifteen neurons (5%) responded phasically to arm extension toward the bar, 124 (excitation 88, inhibition 36, 45%) during bar press (BP), and 91 (excitation 32, inhibition 59, 33%) during ingestion reward (RW). Most BP responses (84/124, 68%) continued tonically throughout the BP period with no correlation to each BP movement. In 14 neurons (14/124, 11%), firing showed a specific variation: transient early BP responses shifted to tonic steady ones in palatable food trials, and the shifts correlated well with BP speed. In 20 other neurons, firing increased during BP hip lifting, and at specific vocalization to ask for food; it decreased during food ingestion, drinking and inguino-crural stimulation. Apomorphine administration decreased firing for the first 5-15 min, then increased it with frequent lip smacking, nausea, involuntary movement and vocalization. Thus VTA neurons showed mostly steady tonic responses but some specific phasic responses. They responded not only to motor events but also in close relation to changes of motivational aspects. Neuronal responses were excitation during procurement of reward and inhibition during or after perception of reward. This modulation in firing, might be important in the initiation and execution of movement and/or motivated 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.     

Amygdaloid neuronal responses to complex visual stimuli in an operant feeding situation in the monkey

In chronically prepared monkeys, 337 neurons were recorded from the anterolateral amygdala during an operant task that required visual discrimination. Twelve percent (39/337) of the neurons responded to one or more of food or non-food visual stimuli. A subset of these responsive neurons was selectively sensitive to the sight of non-food objects with aversive associations. Simultaneous presentation of a food stimulus with the aversive object inhibited the response of these neurons. These response characteristics could not be explained by simple sensory processing of the visual stimuli. It is suggested that the amygdala plays an important role in the elaboration of motivational behavior by using the complex or associative properties of visual stimuli.     

Modulation during learning of the responses of neurons in the lateral hypothalamus to the sight of food

Recordings were made from single neurons in the lateral hypothalamus and substantia innominata of the rhesus and squirrel monkey during feeding. A population of these neurons which altered their firing rates while the monkeys looked at food but not at nonfood objects was investigated. Because the responses of these neurons must have been affected by the previous experience of the animals, the activity of the neurons was measured during tasks in which the monkeys learned whether or not objects which they saw were associated with food. During visual discrimination tests these neurons came to respond when the monkey saw one stimulus associated with food (e.g., a black syringe from which the animal was fed glucose), but not when the monkey saw a different stimulus which was not associated with food (e.g., a white syringe from which the animal was offered saline). During extinction tests these units ceased to respond when the monkey saw a visual stimulus such as a peanut if the peanut was repeatedly not given to the monkey to eat. The learning or extinction behavior approximately paralleled the response of the neurons.The findings that the neurons in the lateral hypothalamus and substantia innominata respond when a monkey is shown food only if he is hungry, and as shown here, if as a result of learning the visual stimulus signifies food, provide information on a part of the brain which may be involved in feeding. The findings are consistent with other data which suggest that the responses of these neurons are involved in the autonomic and/or behavioral reactions of the animal to the sight of food.     

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.     

Catecholaminergic mechanisms of feeding-related lateral hypothalamic activity in the monkey

The functional role of the catecholaminergic mechanism in the lateral hypothalamus (LHA), in feeding behavior of the monkey was investigated by single neuron activity recording and electrophoretic application of dopamine (DA), noradrenaline (NA) and their antagonists. The feeding paradigm had 4 phases: cue light (CL) signaled start of bar press; bar press (BP, 20-30 times); short cue tone (CT) triggered by last bar press signaled presentation of food; and ingestion-reward (RW). Of 312 neurons tested, 189 (61%) responded in one or more phases of the feeding task. Two types of response were observed: CL- or CT-related transient, and BP- or RW-related long-lasting responses. These feeding-related responses depended on the nature of the food and on the hunger-satiety level. DA excited or inhibited different neurons, while NA mainly inhibited firing. DA-sensitive neurons responded more often in the feeding task than insensitive neurons due mainly to differences in responsiveness to CL on (chi 2 test, P less than 0.01), at motor initiation, and during BP (P less than 0.05). Spiperone blocked the former two responses. NA-sensitive neurons responded more often in the feeding task due to responsiveness during BP and RW (P less than 0.01). Sotalol blocked some BP-related responses, and phenoxybenzamine and sotalol blocked the CT-related responses. The data suggest that dopaminergic and noradrenergic inputs in the LHA are crucial in task initiation and reward processing, respectively. Integration of these catecholaminergic and other inputs in the LHA might be important in accomplishing motivated feeding.     

Internal and external information processing by lateral hypothalamic glucose-sensitive and insensitive neurons during bar press feeding in the monkey

Single neuron activities in the lateral hypothalamic area (LHA) were recorded during bar press feeding task in the monkey. First registered neurons were sorted into 2 groups, glucose-sensitive (GS) and glucose-insensitive (GIS) neurons, depending on their glucose sensitivity. Then firing variations to feeding, electrophoretically applied catecholamines and opiate, and to odor and taste stimuli were investigated. GS neurons responded to dopamine, noradrenaline and morphine more often than GIS neurons. In feeding task GS neurons responded during bar press (BP) and reward (RW) periods with long-lasting inhibition of firing and at cue tone (CT) with transient inhibition, while GIS neurons responded during BP and RW periods mainly with excitation and at cue light (CL) with excitation. A majority of GS neurons responded to both odor and taste stimuli more often than GIS neurons. Data suggest that these two kinds of neurons in the LHA may be involved in different functional aspects of feeding: GS neurons, mainly in internal information processing and reward mechanism, and GIS neurons, in external information processing and motor aspects.     

Neuronal activity in the medial orbitofrontal cortex of the behaving monkey: Modulation by glucose and satiety

To investigate neuronal responses to interoceptive information, single neuron activity of the orbitofrontal cortex (OBF) of the behaving monkey was recorded during glucose injection, natural feeding and an operant bar press feeding task. Intravenous glucose injection had almost no effect on rates of spontaneous firing, but tended to attenuate neuronal responses during the bar press and reward periods. In about half of the neurons tested, the spontaneous firing rate changed for a relatively long period after the animal ate to satiety. The results suggest that blood glucose concentration is a modulatory factor in neuronal processing for feeding, but other interoceptive information generated by satiety strongly affects the activity of OBF neurons.     

Visual responses of neurons in the dorsolateral amygdala of the alert monkey

There is evidence that the inferotemporal visual cortex in the monkey projects to the amygdala, and evidence that damage to this region impairs the learning of associations between visual stimuli and reward or punishment. In recordings made in the amygdala to determine whether or not visual responses were found, and if so how they were affected by the significance of the visual stimuli, neurons were found in the dorsolateral part of the amygdala with visual responses which in most cases were sustained while the animal looked at effective visual stimuli. The latency of the responses was 100 to 140 ms or more. The majority (85%) of these neurons responded more strongly to some stimuli than to others, but physical factors which accounted for the responses of the neurons, such as shape, size, orientation, color, or texture, could not usually be identified. Although 22 (19.5%) of these neurons responded primarily to food objects, the responses were not uniquely food-related. Furthermore, although some neurons responded in a visual discrimination test to a visual stimulus which indicated reward, and not to a visual stimulus which indicated saline, only minor modifications of the magnitude of the neuronal responses to the stimuli were obtained when the reward-related significance of the stimuli was reversed. The visual responses of these amygdaloid neurons were thus intermediate in some respects between those of neurons in the inferotemporal cortex, which are not affected by the significance of visual stimuli, and those of neurons in a region to which the amygdala projects, the lateral hypothalamus and substantia innominata, where neurons respond to visual stimuli associated with food reward.     

Behavioral significance of monkey hypothalamic glucose-sensitive neurons

Feeding-related neuronal activity of lateral hypothalamic glucose-sensitive and glucose-insensitive neurons was investigated in behaving monkeys. The behavioral paradigm was a high fixed ratio of bar pressing for food reward signaled by light and tone cues. Twenty-seven percent of the neurons tested were glucose-sensitive. The population of neurons which changed in firing rate during the feeding task was higher among glucose-sensitive cells than among glucose-insensitive cells. The activity of many glucose-sensitive neurons decreased during the bar pressing and reward periods. A small population of glucose-sensitive neurons responded to cue stimuli. The results suggest that glucose-sensitive neurons are mainly involved in the drive and/or reward mechanism of feeding behavior, and that these cells may have specific roles in neural control of hunger-motivated food acquisition.