Subthalamic nucleus physiology is correlated with deep brain stimulation motor and non-motor outcomes.

Subthalamic nucleus deep brain stimulation is commonly indicated for symptomatic relief of idiopathic Parkinson's disease. Despite the known improvement in motor scores, affective, cognitive, voice and speech functions might deteriorate following this procedure. Recent studies have correlated motor outcomes with intraoperative microelectrode recordings. However, there are no microelectrode recording-based tools with predictive values relating to long-term outcomes of integrative motor and non-motor symptoms. We conducted a retrospective analysis of the outcomes of patients with idiopathic Parkinson's disease who had subthalamic nucleus deep brain stimulation at Tel Aviv Sourasky Medical Centre (Tel Aviv, Israel) during 2015-2016. Forty-eight patients (19 women, 29 men; mean age, 58 ± 8 years) who were implanted with a subthalamic nucleus deep brain stimulation device underwent pre- and postsurgical assessments of motor, neuropsychological, voice and speech symptoms. Significant improvements in all motor symptoms (except axial signs) and levodopa equivalent daily dose were noted in all patients. Mild improvements were observed in more posterior-related neuropsychological functions (verbal memory, visual memory and organization) while mild deterioration was observed in frontal functions (personality changes, executive functioning and verbal fluency). The concomitant decline in speech intelligibility was mild and only partial, probably in accordance with the neuropsychological verbal fluency results. Acoustic characteristics were the least affected and remained within normal values. Dimensionality reduction of motor, neuropsychological and voice scores rendered six principal components that reflect the main clinical aspects: the tremor-dominant versus the rigidity-bradykinesia-dominant motor symptoms, frontal versus posterior neuropsychological deficits and acoustic characteristics versus speech intelligibility abnormalities. Microelectrode recordings of subthalamic nucleus spiking activity were analysed off-line and correlated with the original scores and with the principal component results. Based on 198 microelectrode recording trajectories, we suggest an intraoperative subthalamic nucleus deep brain stimulation score, which is a simple sum of three microelectrode recording properties: normalized neuronal activity, the subthalamic nucleus width and the relative proportion of the subthalamic nucleus dorsolateral oscillatory region. A threshold subthalamic nucleus deep brain stimulation score >2.5 (preferentially composed of normalized root mean square >1.5, subthalamic nucleus width >3 mm and a dorsolateral oscillatory region/subthalamic nucleus width ratio >1/3) predicts better motor and non-motor long-term outcomes. The algorithm presented here optimizes intraoperative decision-making of deep brain stimulation contact localization based on microelectrode recording with the aim of improving long-term (>1 year) motor, neuropsychological and voice symptoms.

Distinct Progressions of Neuronal Activity Changes Underlie the Formation and Consolidation of a Gustatory Associative Memory.

Acquiring new memories is a multistage process. Numerous studies have convincingly demonstrated that initially acquired memories are labile and are stabilized only by later consolidation processes. These multiple phases of memory formation are known to involve modification of both cellular excitability and synaptic connectivity, which in turn change neuronal activity at both the single neuron and ensemble levels. However, the specific mapping between the known phases of memory and the changes in neuronal activity at different organizational levels-the single-neuron, population representations, and ensemble-state dynamics-remains unknown. Here we address this issue in the context of conditioned taste aversion learning by continuously tracking gustatory cortex neuronal taste responses in alert male and female rats during the 24 h following a taste-malaise pairing. We found that the progression of activity changes depends on the neuronal organizational level: whereas the population response changed continuously, the population mean response amplitude and the number of taste-responsive neurons only increased during the acquisition and consolidation phases. In addition, the known quickening of the ensemble-state dynamics associated with the faster rejection of harmful foods appeared only after consolidation. Overall, these results demonstrate how complex dynamics in the different representational levels of cortical activity underlie the formation and stabilization of memory within the cortex.SIGNIFICANCE STATEMENT Memory formation is a multiphased process; early acquired memories are labile and consolidate to their stable forms over hours and days. The progression of memory is assumed to be supported by changes in neuronal activity, but the mapping between memory phases and neuronal activity changes remains elusive. Here we tracked cortical neuronal activity over 24 h as rats acquired and consolidated a taste-malaise association memory, and found specific differences between the progression at the single-neuron and populations levels. These results demonstrate how balanced changes on the single-neuron level lead to changes in the network-level representation and dynamics required for the stabilization of memories.

ApoE4 attenuates cortical neuronal activity in young behaving apoE4 rats.

The E4 allele of apolipoprotein E (apoE4) is the strongest genetic risk factor for late-onset Alzheimer's disease (AD). However, apoE4 may cause innate brain abnormalities before the appearance of AD-related neuropathology. Understanding these primary dysfunctions is vital for the early detection of AD and the development of therapeutic strategies. Recently we reported impaired extra-hippocampal memory in young apoE4 mice, a deficit that was correlated with attenuated structural pre-synaptic plasticity in cortical and subcortical regions. Here we tested the hypothesis that these early structural deficits impact learning via changes in basal and stimuli evoked neuronal activity. We recorded extracellular neuronal activity from the gustatory cortex (GC) of three-month-old humanized apoE4 (hApoE4) and wildtype rats expressing rat apoE (rAE), before and after conditioned taste aversion (CTA) training. Despite normal sucrose drinking behavior before CTA, young hApoE4 rats showed impaired CTA learning, consistent with our previous results in target-replacement apoE4 mice. This behavioral deficit was correlated with decreased basal and taste-evoked firing rates in both putative excitatory and inhibitory GC neurons. Further taste coding analyses at the single neuron and ensemble levels revealed that GC neurons of the hApoE4 group correctly classified tastes, but were unable to undergo plasticity to support learning. These results suggest that apoE4 impacts brain excitability and plasticity early in life that may act as an initiator for later AD pathologies.

Temporally-precise basolateral amygdala activation is required for the formation of taste memories in gustatory cortex.

KEY POINTS: The basolateral amygdala (BLA), the nucleus basalis magnocellularis (NBM), and the gustatory cortex (GC) are involved in taste processing, taste memory formation and conditioned taste aversion (CTA) learning, but their fine-temporal interactions that support these cognitive functions are not well understood. We found that the formation of novel-taste and CTA memories in the GC depend on a distinct late response (700-3000 ms) of BLA projection neurons. In contrast, BLA activity was not essential for palatability-related behaviour and coding in the GC prior to CTA. We identified the BLA→NBM pathway as a potential pathway for the transmission of taste novelty information, required for the formation of taste and CTA memories in the GC. Our results demonstrate how neuronal dynamics across multiple brain regions support long-term memory formation. ABSTRACT: Learning to associate malaise with the intake of novel food is critical for survival. Since food poisoning may take hours to take effect, animals developed brain circuits to transform the current novel taste experience into a taste memory trace (TMT) and bridge this time lag. Ample studies showed that the basolateral amygdala (BLA), the nucleus basalis magnocellularis (NBM) and the gustatory cortex (GC) are involved in TMT formation and taste-malaise association. However, how dynamic activity across these brain regions during novel taste experience promotes the formation of these memories is currently unknown. We used the conditioned taste aversion (CTA) learning paradigm in combination with short-term optogenetics and electrophysiological recording in rats to test the hypothesis that temporally specific activation of BLA projection neurons is essential for TMT formation in the GC, and consequently CTA. We found that a short late epoch (LE, 700-3000 ms), but not the early epoch (EE, 0-500 ms), of BLA activation during novel taste experience is essential for normal CTA, for early c-Fos expression in the GC (a marker of TMT formation) and for the post-CTA changes in GC ensemble palatability coding. Interestingly, BLA activity was not required for intact taste identity or palatability perceptions before CTA. We further show that BLA-LE information is transmitted to GC through the BLA→NBM pathway where it affects the formation of taste memories. These results expose the dependence of long-term memory formation on specific temporal windows during sensory responses and the distributed circuits supporting this dependence.

Extra-Hippocampal Learning Deficits in Young Apolipoprotein E4 Mice and Their Synaptic Underpinning.

The E4 allele of apolipoprotein (apoE4) is the primary genetic risk factor for late onset Alzheimer's disease (AD), yet the exact manner in which apoE4 leads to the development of AD is undetermined. Human and animal studies report that apoE4-related memory deficits appear earlier than the AD clinical manifestation, thus suggesting the existence of early, pre-pathological, apoE4 impairments that may later lead to AD onset. While current research regards the hippocampus as the initial and primary effected locus by apoE4, we presently investigate the possibility that apoE4 innately impairs any brain area that requires synaptic plasticity. To test this hypothesis, we trained young (3-4-month-old) target-replacement apoE3 and apoE4 mice in conditioned taste aversion (CTA) acquisition and extinction learnings- hippocampus-independent learnings that are easily performed at a young age. Synaptic vesicular markers analysis was conducted in the gustatory cortex (GC), basolateral amygdala (BLA), medial prefrontal cortex (mPFC), and hippocampal CA3 to reveal underlying apoE4-related impairments. We have found that young apoE4 mice are severely impaired in CTA acquisition and extinction learning. CTA acquisition impairments were correlated with reduced vGat and vGlut levels in the BLA and GC, but not in the CA3. CTA extinction was correlated with lower synaptophysin and vGlut levels in the mPFC, a central region in CTA extinction. Our results support apoE4-related early-life plasticity impairments that precede the AD clinical manifestations and affect any brain area that depends on extensive plasticity; early impairments that may promote the development of AD pathologies later in life.

Beta oscillations in the parkinsonian primate: Similar oscillations across different populations.

Parkinson's disease (PD) is characterized by excessive beta band oscillations (BBO) in neuronal spiking activity across basal ganglia (BG) nuclei. High frequency stimulation of the subthalamic nucleus, an effective treatment for PD, suppresses these oscillations. There is still a heated debate on the origin and propagation of BBO and their association to clinical symptoms. The key prerequisite in addressing these issues is to obtain an accurate estimation of the subpopulation of oscillatory neurons and the magnitude of their oscillations. Studies have shown that neurons in different BG nuclei vary dramatically in the magnitude of their oscillations. However, the stochastic nature of neuronal activity subsamples the oscillatory neuronal rate functions, thus causing standard spectral analysis methods to be dramatically biased by biological and experimental factors such as variations in the neuronal firing rate across BG nuclei. In order to overcome these biases, and directly analyze the expression of BBO within BG nuclei, we used a novel objective method, the modulation index. This method reveals that unlike previous spectral results, individual neurons in the different nuclei display similar magnitudes of oscillations, whereas only the size of the oscillatory subpopulation varies between nuclei. During stimulation, the magnitude of the BBO does not change but the fraction of oscillatory neurons decreases in the globus pallidus internus, leading to a significant change in BG output. This non-biased oscillation quantification thus enables the reconstruction of oscillations at the single neuron and nuclei population levels, and calls for a reassessment of the role of BBO during PD.

Preexposure to salty and sour taste enhances conditioned taste aversion to novel sucrose.

Conditioned taste aversion (CTA) is an intensively studied single-trial learning paradigm whereby animals are trained to avoid a taste that has been paired with malaise. Many factors influence the strength of aversion learning; prominently studied among these is taste novelty-the fact that preexposure to the taste conditioned stimulus (CS) reduces its associability. The effect of exposure to tastes other than the CS has, in contrast, received little investigation. Here, we exposed rats to sodium chloride (N) and citric acid (C), either before or within a conditioning session involving novel sucrose (S). Presentation of this taste array within the conditioning session weakened the resultant S aversion, as expected. The opposite effect, however, was observed when exposure to the taste array was provided in sessions that preceded conditioning: such experience enhanced the eventual S aversion-a result that was robust to differences in CS delivery method and number of tastes presented in conditioning sessions. This "non-CS preexposure effect" scaled with the number of tastes in the exposure array (experience with more stimuli was more effective than experience with fewer) and with the amount of exposure sessions (three preexposure sessions were more effective than two). Together, our results provide evidence that exposure and experience with the realm of tastes changes an animal's future handling of even novel tastes.

Dynamic taste responses of parabrachial pontine neurons in awake rats.

The parabrachial nuclei of the pons (PbN) receive almost direct input from taste buds on the tongue and control basic taste-driven behaviors. Thus it is reasonable to hypothesize that PbN neurons might respond to tastes in a manner similar to that of peripheral receptors, i.e., that these responses might be narrow and relatively "dynamics free." On the other hand, the majority of the input to PbN descends from forebrain regions such as gustatory cortex (GC), which processes tastes with "temporal codes" in which firing reflects first the presence, then the identity, and finally the desirability of the stimulus. Therefore a reasonable alternative hypothesis is that PbN responses might be dominated by dynamics similar to those observed in GC. Here we examined simultaneously recorded single-neuron PbN (and GC) responses in awake rats receiving exposure to basic taste stimuli. We found that pontine taste responses were almost entirely confined to canonically identified taste-PbN (t-PbN). Taste-specificity was found, furthermore, to be time varying in a larger percentage of these t-PbN responses than in responses recorded from the tissue around PbN (including non-taste-PbN). Finally, these time-varying properties were a good match for those observed in simultaneously recorded GC neurons-taste-specificity appeared after an initial nonspecific burst of action potentials, and palatability emerged several hundred milliseconds later. These results suggest that the pontine taste relay is closely allied with the dynamic taste processing performed in forebrain.

Sensory cortical population dynamics uniquely track behavior across learning and extinction.

Neural responses in many cortical regions encode information relevant to behavior: information that necessarily changes as that behavior changes with learning. Although such responses are reasonably theorized to be related to behavior causation, the true nature of that relationship cannot be clarified by simple learning studies, which show primarily that responses change with experience. Neural activity that truly tracks behavior (as opposed to simply changing with experience) will not only change with learning but also change back when that learning is extinguished. Here, we directly probed for this pattern, recording the activity of ensembles of gustatory cortical single neurons as rats that normally consumed sucrose avidly were trained first to reject it (i.e., conditioned taste aversion learning) and then to enjoy it again (i.e., extinction), all within 49 h. Both learning and extinction altered cortical responses, consistent with the suggestion (based on indirect evidence) that extinction is a novel form of learning. But despite the fact that, as expected, postextinction single-neuron responses did not resemble "naive responses," ensemble response dynamics changed with learning and reverted with extinction: both the speed of stimulus processing and the relationships among ensemble responses to the different stimuli tracked behavioral relevance. These data suggest that population coding is linked to behavior with a fidelity that single-neuron coding is not.

Haloperidol-induced changes in neuronal activity in the striatum of the freely moving rat.

The striatum is the main input structure of the basal ganglia, integrating input from the cerebral cortex and the thalamus, which is modulated by midbrain dopaminergic input. Dopamine modulators, including agonists and antagonists, are widely used to relieve motor and psychiatric symptoms in a variety of pathological conditions. Haloperidol, a dopamine D2 antagonist, is commonly used in multiple psychiatric conditions and motor abnormalities. This article reports the effects of haloperidol on the activity of three major striatal subpopulations: medium spiny neurons (MSNs), fast spiking interneurons (FSIs), and tonically active neurons (TANs). We implanted multi-wire electrode arrays in the rat dorsal striatum and recorded the activity of multiple single units in freely moving animals before and after systemic haloperidol injection. Haloperidol decreased the firing rate of FSIs and MSNs while increasing their tendency to fire in an oscillatory manner in the high voltage spindle (HVS) frequency range of 7-9 Hz. Haloperidol led to an increased firing rate of TANs but did not affect their non-oscillatory firing pattern and their typical correlated firing activity. Our results suggest that dopamine plays a key role in tuning both single unit activity and the interactions within and between different subpopulations in the striatum in a differential manner. These findings highlight the heterogeneous striatal effects of tonic dopamine regulation via D2 receptors which potentially enable the treatment of diverse pathological states associated with basal ganglia dysfunction.

Changes in basal ganglia processing of cortical input following magnetic stimulation in Parkinsonism.

Parkinsonism is associated with major changes in neuronal activity throughout the cortico-basal ganglia loop. Current measures quantify changes in baseline neuronal and network activity but do not capture alterations in information propagation throughout the system. Here, we applied a novel non-invasive magnetic stimulation approach using a custom-made mini-coil that enabled us to study transmission of neuronal activity throughout the cortico-basal ganglia loop in both normal and parkinsonian primates. By magnetically perturbing cortical activity while simultaneously recording neuronal responses along the cortico-basal ganglia loop, we were able to directly investigate modifications in descending cortical activity transmission. We found that in both the normal and parkinsonian states, cortical neurons displayed similar multi-phase firing rate modulations in response to magnetic stimulation. However, in the basal ganglia, large synaptically driven stereotypic neuronal modulation was present in the parkinsonian state that was mostly absent in the normal state. The stimulation-induced neuronal activity pattern highlights the change in information propagation along the cortico-basal ganglia loop. Our findings thus point to the role of abnormal dynamic activity transmission rather than changes in baseline activity as a major component in parkinsonian pathophysiology. Moreover, our results hint that the application of transcranial magnetic stimulation (TMS) in human patients of different disorders may result in different neuronal effects than the one induced in normal subjects.

Inactivation of basolateral amygdala specifically eliminates palatability-related information in cortical sensory responses.

Evidence indirectly implicates the amygdala as the primary processor of emotional information used by cortex to drive appropriate behavioral responses to stimuli. Taste provides an ideal system with which to test this hypothesis directly, as neurons in both basolateral amygdala (BLA) and gustatory cortex (GC)-anatomically interconnected nodes of the gustatory system-code the emotional valence of taste stimuli (i.e., palatability), in firing rate responses that progress similarly through "epochs." The fact that palatability-related firing appears one epoch earlier in BLA than GC is broadly consistent with the hypothesis that such information may propagate from the former to the latter. Here, we provide evidence supporting this hypothesis, assaying taste responses in small GC single-neuron ensembles before, during, and after temporarily inactivating BLA in awake rats. BLA inactivation (BLAx) changed responses in 98% of taste-responsive GC neurons, altering the entirety of every taste response in many neurons. Most changes involved reductions in firing rate, but regardless of the direction of change, the effect of BLAx was epoch-specific: while firing rates were changed, the taste specificity of responses remained stable; information about taste palatability, however, which normally resides in the "Late" epoch, was reduced in magnitude across the entire GC sample and outright eliminated in most neurons. Only in the specific minority of neurons for which BLAx enhanced responses did palatability specificity survive undiminished. Our data therefore provide direct evidence that BLA is a necessary component of GC gustatory processing, and that cortical palatability processing in particular is, in part, a function of BLA activity.

Dynamic stereotypic responses of Basal Ganglia neurons to subthalamic nucleus high-frequency stimulation in the parkinsonian primate.

Deep brain stimulation (DBS) in the subthalamic nucleus (STN) is a well-established therapy for patients with severe Parkinson's disease (PD); however, its mechanism of action is still unclear. In this study we explored static and dynamic activation patterns in the basal ganglia (BG) during high-frequency macro-stimulation of the STN. Extracellular multi-electrode recordings were performed in primates rendered parkinsonian using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Recordings were preformed simultaneously in the STN and the globus pallidus externus and internus. Single units were recorded preceding and during the stimulation. During the stimulation, STN mean firing rate dropped significantly, while pallidal mean firing rates did not change significantly. The vast majority of neurons across all three nuclei displayed stimulation driven modulations, which were stereotypic within each nucleus but differed across nuclei. The predominant response pattern of STN neurons was somatic inhibition. However, most pallidal neurons demonstrated synaptic activation patterns. A minority of neurons across all nuclei displayed axonal activation. Temporal dynamics were observed in the response to stimulation over the first 10 seconds in the STN and over the first 30 seconds in the pallidum. In both pallidal segments, the synaptic activation response patterns underwent delay and decay of the magnitude of the peak response due to short term synaptic depression. We suggest that during STN macro-stimulation the STN goes through a functional ablation as its upper bound on information transmission drops significantly. This notion is further supported by the evident dissociation between the stimulation driven pre-synaptic STN somatic inhibition and the post-synaptic axonal activation of its downstream targets. Thus, BG output maintains its firing rate while losing the deleterious effect of the STN. This may be a part of the mechanism leading to the beneficial effect of DBS in PD.

Generalized framework for stimulus artifact removal.

Stimulation is extensively used in neuroscience research in diverse fields ranging from cognitive to clinical. Studying the effect of electrical and magnetic stimulation on neuronal activity is complicated by large stimulation-derived artifacts on the recording electrodes, which mask the spiking activity. Multiple studies have suggested a variety of solutions for the removal of artifacts and were typically directed at specific stimulation setups. In this study we introduce a generalized framework for stimulus artifacts removal, the Stimulus Artifact Removal Graphical Environment (SARGE). The framework provides an encapsulated environment for a multi-stage removal process, starting from the stimulus pulse detection, through estimation of the artifacts and their removal, and finally to signal reconstruction and the assessment of removal quality. The framework provides the user with subjective graphical and objective quantitative tools for assessing the resulting signal, and the ability to adjust the process to optimize the results. This extendable publicly available framework supports different types of stimulation, stimulation patterns and shapes, and a variety of artifact estimation methods. We exemplify the removal of artifacts generated by electrical micro- and macro-stimulation and magnetic stimulation and different stimulation protocols. The use of different estimation methods, such as averaging and function fitting is demonstrated, and the differences between them are discussed. Finally, the quality of removal is assessed and validated using quantitative measures and combined experimental-simulation studies. The framework marks a shift from "algorithm" and "data" centric approach to a "workflow" centric approach, thus introducing an innovative concept to the artifact removal process.

Effects of trial repetition in texture discrimination.

Performance on the texture discrimination task improves with practice but was also shown to decrease between closely spaced sessions. Here we explored immediate changes in performance within a single session. We found that, after an initial increase, performance declined with further training within a single session. This deterioration in performance was smaller when the inter-trial interval was longer than 3s. Performance recovered when targets were presented in new locations within the texture stimulus-thereby excluding a general fatigue process or adaptation to the stimulus light-intensity as an explanation for our findings. Further, the complete transfer of deterioration between eyes pointed to cortical origin. Deterioration was also found for task-irrelevant targets, indicating the involvement of a sensory mechanism. Collectively, these findings trace the deterioration of performance in the texture discrimination task, previously observed across several hours, to cortical events occurring during or immediately after stimulus presentation.

Real-time refinement of subthalamic nucleus targeting using Bayesian decision-making on the root mean square measure.

The subthalamic nucleus (STN) is a major target for treatment of advanced Parkinson's disease patients undergoing deep brain stimulation surgery. Microelectrode recording (MER) is used in many cases to identify the target nucleus. A real-time procedure for identifying the entry and exit points of the STN would improve the outcome of this targeting procedure. We used the normalized root mean square (NRMS) of a short (5 seconds) MER sampled signal and the estimated anatomical distance to target (EDT) as the basis for this procedure. Electrode tip location was defined intraoperatively by an expert neurophysiologist to be before, within, or after the STN. Data from 46 trajectories of 27 patients were used to calculate the Bayesian posterior probability of being in each of these locations, given RMS-EDT pair values. We tested our predictions on each trajectory using a bootstrapping technique, with the rest of the trajectories serving as a training set and found the error in predicting the STN entry to be (mean +/- SD) 0.18 +/- 0.84, and 0.50 +/- 0.59 mm for STN exit point, which yields a 0.30 +/- 0.28 mm deviation from the expert's target center. The simplicity and computational ease of RMS calculation, its spike sorting-independent nature and tolerance to electrode parameters of this Bayesian predictor, can lead directly to the development of a fully automated intraoperative physiological procedure for the refinement of imaging estimates of STN borders.